diff --git a/crates/oxide_emit/src/expr/assignment.rs b/crates/oxide_emit/src/expr/assignment.rs
index b6e1f6d5..fe72159b 100644
--- a/crates/oxide_emit/src/expr/assignment.rs
+++ b/crates/oxide_emit/src/expr/assignment.rs
@@ -214,22 +214,97 @@ impl Emitter {
                 self.emit_computed_member_dynamic(assign, member, ctx)
             }
         } else if let oxide_parser::AssignmentTarget::PrivateFieldExpression(member) = &assign.left {
-            if assign.operator != AssignmentOperator::Assign {
-                return Err("compound assignment to private fields not supported".into());
+            let name = member.field.name.as_str();
+            // 逻辑赋值：GET_PRIVATE 读旧值（brand 检查在读时执行）→ 短路测试 →
+            // 通过才求值 RHS 并 SET_PRIVATE 写回，结果统一为旧值或新值。
+            if let Some(logical_op) = assign.operator.to_logical_operator() {
+                let store_label = ctx.next_label_id();
+                let end_label = ctx.next_label_id();
+                let obj_reg = self.emit_expression(&member.object, ctx)?;
+                let (brand_reg, brand_id) = self.private_access_brand(obj_reg, name, ctx)?;
+                let key_reg = self.emit_private_id_reg(name, ctx)?;
+                let result_reg = ctx.alloc_reg();
+                ctx.inst(Inst::get_private(
+                    Operand::Reg(result_reg),
+                    Operand::Reg(obj_reg),
+                    Operand::Reg(key_reg),
+                    brand_reg,
+                    brand_id,
+                ));
+                self.emit_logical_assign_test(logical_op, result_reg, store_label, end_label, ctx)?;
+                ctx.labels.set_label_pos(store_label, ctx.insts.len());
+                let val_reg = self.emit_expression(&assign.right, ctx)?;
+                ctx.inst(Inst::set_private(
+                    Operand::Reg(obj_reg),
+                    Operand::Reg(val_reg),
+                    Operand::Reg(key_reg),
+                    brand_reg,
+                    brand_id,
+                ));
+                ctx.inst(Inst::new(
+                    OpCode::LOAD_VAR,
+                    Operand::Reg(result_reg),
+                    Operand::Reg(val_reg),
+                    Operand::None,
+                ));
+                ctx.labels.set_label_pos(end_label, ctx.insts.len());
+                return Ok(result_reg);
             }
             let obj_reg = self.emit_expression(&member.object, ctx)?;
-            let val_reg = self.emit_expression(&assign.right, ctx)?;
-            let name = member.field.name.as_str();
             let (brand_reg, brand_id) = self.private_access_brand(obj_reg, name, ctx)?;
             let key_reg = self.emit_private_id_reg(name, ctx)?;
-            ctx.inst(Inst::set_private(
-                Operand::Reg(obj_reg),
-                Operand::Reg(val_reg),
-                Operand::Reg(key_reg),
-                brand_reg,
-                brand_id,
-            ));
-            Ok(val_reg)
+            if assign.operator != AssignmentOperator::Assign {
+                // 复合赋值保规范求值序：先 GET_PRIVATE 读旧值（brand 检查先于 RHS 副作用），
+                // 再求值 RHS，运算后 SET_PRIVATE 写回。
+                let val_reg = ctx.alloc_reg();
+                ctx.inst(Inst::get_private(
+                    Operand::Reg(val_reg),
+                    Operand::Reg(obj_reg),
+                    Operand::Reg(key_reg),
+                    brand_reg,
+                    brand_id,
+                ));
+                let rhs = self.emit_expression(&assign.right, ctx)?;
+                let op = match assign.operator {
+                    AssignmentOperator::Addition => OpCode::ADD,
+                    AssignmentOperator::Subtraction => OpCode::SUB,
+                    AssignmentOperator::Multiplication => OpCode::MUL,
+                    AssignmentOperator::Division => OpCode::DIV,
+                    AssignmentOperator::Remainder => OpCode::MOD,
+                    AssignmentOperator::Exponential => OpCode::COMPOUND_EXP,
+                    AssignmentOperator::BitwiseAnd => OpCode::BIT_AND,
+                    AssignmentOperator::BitwiseOR => OpCode::BIT_OR,
+                    AssignmentOperator::BitwiseXOR => OpCode::BIT_XOR,
+                    AssignmentOperator::ShiftLeft => OpCode::SHL,
+                    AssignmentOperator::ShiftRight => OpCode::SHR,
+                    AssignmentOperator::ShiftRightZeroFill => OpCode::USHR,
+                    _ => return Err(format!("compound assignment operator {:?} not supported", assign.operator)),
+                };
+                if assign.operator == AssignmentOperator::Exponential {
+                    // 指数无独立二元指令，COMPOUND_EXP 语义 rd=rd^a：rhs 放 a 槽。
+                    ctx.inst(Inst::new(op, Operand::Reg(val_reg), Operand::Reg(rhs), Operand::None));
+                } else {
+                    ctx.inst(Inst::new(op, Operand::Reg(val_reg), Operand::Reg(val_reg), Operand::Reg(rhs)));
+                }
+                ctx.inst(Inst::set_private(
+                    Operand::Reg(obj_reg),
+                    Operand::Reg(val_reg),
+                    Operand::Reg(key_reg),
+                    brand_reg,
+                    brand_id,
+                ));
+                Ok(val_reg)
+            } else {
+                let val_reg = self.emit_expression(&assign.right, ctx)?;
+                ctx.inst(Inst::set_private(
+                    Operand::Reg(obj_reg),
+                    Operand::Reg(val_reg),
+                    Operand::Reg(key_reg),
+                    brand_reg,
+                    brand_id,
+                ));
+                Ok(val_reg)
+            }
         } else if let oxide_parser::AssignmentTarget::AssignmentTargetIdentifier(id_ref) = &assign.left {
             if assign.operator != AssignmentOperator::Assign {
                 if let Some(logical_op) = assign.operator.to_logical_operator() {
diff --git a/crates/oxide_vm/tests/class_tests.rs b/crates/oxide_vm/tests/class_tests.rs
index 6cf59bce..64293bb7 100644
--- a/crates/oxide_vm/tests/class_tests.rs
+++ b/crates/oxide_vm/tests/class_tests.rs
@@ -637,3 +637,176 @@ fn class_generator_method_return_closes_with_value() {
     .unwrap();
     assert_eq!(vm.lookup_str(result).unwrap(), "1,99,true");
 }
+
+// ── 私有字段复合赋值（+= 等）与逻辑赋值（&&= ||= ??=）──
+
+// data 字段复合赋值：旧值读取 → 运算 → 写回，表达式结果与后续读取一致。
+#[test]
+fn private_field_compound_assignment_writes_back() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 1; m(){ return this.#x += 2; } get(){ return this.#x; } } var c = new C(); c.m()*10 + c.get()",
+    )
+    .unwrap();
+    assert_num(result, 33.0);
+}
+
+// 复合赋值先读旧值再求值 RHS：RHS 改写同一字段时仍以旧值参与运算。
+#[test]
+fn private_field_compound_assignment_reads_old_value_before_rhs() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 1; m(){ return this.#x += (this.#x = 5); } get(){ return this.#x; } } var c = new C(); c.m()*10 + c.get()",
+    )
+    .unwrap();
+    // 旧值 1 先读，RHS 把 #x 写为 5，1+5=6 再写回 → 结果 6。
+    assert_num(result, 66.0);
+}
+
+// 减法/乘法/除法复合赋值序列，验证三操作数二元运算路径。
+#[test]
+fn private_field_compound_assignment_arithmetic_operators() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 10; a(){ return this.#x -= 3; } b(){ return this.#x *= 2; } c(){ return this.#x /= 4; } } var c = new C(); c.a()*10000 + c.b()*100 + c.c()",
+    )
+    .unwrap();
+    assert_num(result, 7.0 * 10000.0 + 14.0 * 100.0 + 3.5);
+}
+
+// 位与/左移/位或复合赋值序列。
+#[test]
+fn private_field_compound_assignment_bitwise_and_shift() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 0b1010; a(){ return this.#x &= 0b1100; } b(){ return this.#x <<= 1; } c(){ return this.#x |= 0b1; } } var c = new C(); c.a()*100 + c.b()*10 + c.c()",
+    )
+    .unwrap();
+    assert_num(result, 8.0 * 100.0 + 16.0 * 10.0 + 17.0);
+}
+
+// 指数复合赋值走 COMPOUND_EXP（rhs 在 a 槽）。
+#[test]
+fn private_field_exponential_compound_assignment() {
+    let mut vm = Vm::new();
+    let result = eval(&mut vm, "class C { #x = 2; m(){ return this.#x **= 3; } } new C().m()").unwrap();
+    assert_num(result, 8.0);
+}
+
+// 私有访问器复合赋值：getter 读旧值、setter 写新值。
+#[test]
+fn private_accessor_compound_assignment_uses_getter_setter() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { static get #x(){ return this._v; } static set #x(v){ this._v = v; } static m(){ this.#x = 1; return this.#x += 2; } static get(){ return this._v; } } C.m()*10 + C.get()",
+    )
+    .unwrap();
+    assert_num(result, 33.0);
+}
+
+// readonly-accessor 复合赋值：无 setter 抛 TypeError。
+#[test]
+fn private_readonly_accessor_compound_assignment_throws_type_error() {
+    let mut vm = Vm::new();
+    let err = eval(
+        &mut vm,
+        "class C { static get #x(){ return 1; } static m(){ return this.#x += 1; } } C.m()",
+    )
+    .unwrap_err();
+    assert!(err.contains("TypeError"), "expected TypeError, got: {err}");
+}
+
+// 私有方法槽复合赋值：写方法槽抛 TypeError。
+#[test]
+fn private_method_compound_assignment_throws_type_error() {
+    let mut vm = Vm::new();
+    let err = eval(&mut vm, "class C { #m(){ return 1; } m(){ return this.#m += 1; } } new C().m()").unwrap_err();
+    assert!(err.contains("TypeError"), "expected TypeError, got: {err}");
+}
+
+// 私有方法槽逻辑赋值（&&= 走写回路径）同样抛 TypeError。
+#[test]
+fn private_method_logical_assignment_throws_type_error() {
+    let mut vm = Vm::new();
+    let err = eval(&mut vm, "class C { #m(){ return 1; } m(){ return this.#m &&= 2; } } new C().m()").unwrap_err();
+    assert!(err.contains("TypeError"), "expected TypeError, got: {err}");
+}
+
+// ||= 对 truthy 旧值短路：RHS 副作用不执行，字段保持原值。
+#[test]
+fn private_field_logical_or_keeps_truthy_value_and_short_circuits() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 1; m(){ var n = 0; var r = this.#x ||= ++n; return r*10 + n; } } new C().m()",
+    )
+    .unwrap();
+    // #x=1 为 truthy → 短路，RHS 不执行，结果保持 1。
+    assert_num(result, 10.0);
+}
+
+// ||= 对 falsy 旧值写回 RHS 值。
+#[test]
+fn private_field_logical_or_assigns_when_falsy() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 0; m(){ return this.#x ||= 5; } get(){ return this.#x; } } var c = new C(); c.m()*10 + c.get()",
+    )
+    .unwrap();
+    assert_num(result, 55.0);
+}
+
+// &&= 对 truthy 旧值写回 RHS 值。
+#[test]
+fn private_field_logical_and_assigns_when_truthy() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 1; m(){ return this.#x &&= 2; } get(){ return this.#x; } } var c = new C(); c.m()*10 + c.get()",
+    )
+    .unwrap();
+    assert_num(result, 22.0);
+}
+
+// &&= 对 falsy 旧值短路：RHS 副作用不执行，字段保持原值。
+#[test]
+fn private_field_logical_and_short_circuits_on_falsy() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 0; m(){ var n = 0; var r = this.#x &&= ++n; return r*10 + n; } } new C().m()",
+    )
+    .unwrap();
+    // #x=0 为 falsy → 短路，RHS 不执行，结果保持 0。
+    assert_num(result, 0.0);
+}
+
+// ??= 对 nullish（未初始化字段为 undefined）写回 RHS 值。
+#[test]
+fn private_field_nullish_coalesce_assigns_when_nullish() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x; m(){ return this.#x ??= 7; } get(){ return this.#x; } } var c = new C(); c.m()*10 + c.get()",
+    )
+    .unwrap();
+    assert_num(result, 77.0);
+}
+
+// ??= 对已定义旧值短路：RHS 副作用不执行。
+#[test]
+fn private_field_nullish_coalesce_short_circuits_on_defined() {
+    let mut vm = Vm::new();
+    let result = eval(
+        &mut vm,
+        "class C { #x = 1; m(){ var n = 0; var r = this.#x ??= ++n; return r*10 + n; } } new C().m()",
+    )
+    .unwrap();
+    assert_num(result, 10.0);
+}