diff --git a/crates/oxide_builtins/src/temporal.rs b/crates/oxide_builtins/src/temporal.rs
index fb34cdc7..72fee705 100644
--- a/crates/oxide_builtins/src/temporal.rs
+++ b/crates/oxide_builtins/src/temporal.rs
@@ -2962,6 +2962,72 @@ pub fn plain_date_time_to_string<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeRe
     NativeResult::Ok(vm.new_string(&output))
 }
 
+/// 按 duration-like 分量对 PlainDateTime 做加减：先平衡时间（溢出为天），
+/// 再按年/月/周/日推进日期，最后校验范围。
+fn plain_date_time_apply_duration<H: VmHost>(vm: &mut H, args: &[u8], sign: i64) -> NativeResult {
+    let (year, month, day, time_ns) = match plain_date_time_parts(vm, args) {
+        Ok(parts) => parts,
+        Err(error) => return NativeResult::Err(error),
+    };
+    let val = if args.len() > 1 { vm.reg(args[1]) } else { JsValue::undefined() };
+    let values = match duration_like_values(vm, val) {
+        Ok(values) => values,
+        Err(error) => return NativeResult::Err(error),
+    };
+    let constrain = match plain_date_time_overflow(vm, args) {
+        Ok(constrain) => constrain,
+        Err(error) => return NativeResult::Err(error),
+    };
+    const DAY_NS: i128 = 86_400_000_000_000;
+    // 时间字段（hours 起）单独换算纳秒；days 由日期部分处理，避免重复计入。
+    let [_, _, _, _, h, min, s, ms, us, ns] = values;
+    let time_delta = duration_component_integer(h).unwrap_or(0) * 3_600_000_000_000
+        + duration_component_integer(min).unwrap_or(0) * 60_000_000_000
+        + duration_component_integer(s).unwrap_or(0) * 1_000_000_000
+        + duration_component_integer(ms).unwrap_or(0) * 1_000_000
+        + duration_component_integer(us).unwrap_or(0) * 1_000
+        + duration_component_integer(ns).unwrap_or(0);
+    let total_ns = time_ns as i128 + time_delta * sign as i128;
+    let extra_days = total_ns.div_euclid(DAY_NS);
+    let new_time_ns = total_ns.rem_euclid(DAY_NS);
+
+    let [y, m, w, d, ..] = values;
+    let months =
+        (duration_component_integer(y).unwrap_or(0) * 12 + duration_component_integer(m).unwrap_or(0)) * sign as i128;
+    let total_month = i128::from(year) * 12 + i128::from(month) - 1 + months;
+    let ny = total_month.div_euclid(12);
+    let nm = total_month.rem_euclid(12) + 1;
+    let Some(max_day) = days_in_month(ny, nm) else {
+        return NativeResult::Err(crate::error::create_range_error(vm, "invalid date"));
+    };
+    let day = i128::from(day);
+    let new_day = if day > max_day {
+        if !constrain {
+            return NativeResult::Err(crate::error::create_range_error(vm, "day out of range"));
+        }
+        max_day
+    } else {
+        day
+    };
+    let day_delta = duration_component_integer(w).unwrap_or(0) * 7 + duration_component_integer(d).unwrap_or(0);
+    let total_days = days_from_civil(ny, nm, new_day) + extra_days + day_delta * sign as i128;
+    let (yy, mm, dd) = civil_from_days(total_days);
+    if !valid_plain_date_time_range(yy as i32, mm as u32, dd as u32, new_time_ns as f64) {
+        return NativeResult::Err(crate::error::create_range_error(vm, "invalid date-time"));
+    }
+    make_plain_date_time(vm, yy as i32, mm as u32, dd as u32, new_time_ns as f64)
+}
+
+/// `Temporal.PlainDateTime.prototype.add(durationLike, options)`。
+pub fn plain_date_time_add<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    plain_date_time_apply_duration(vm, args, 1)
+}
+
+/// `Temporal.PlainDateTime.prototype.subtract(durationLike, options)`。
+pub fn plain_date_time_subtract<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    plain_date_time_apply_duration(vm, args, -1)
+}
+
 /// `Temporal.PlainDateTime.prototype.toJSON()`：输出默认 ISO 日期时间。
 pub fn plain_date_time_to_json<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
     plain_date_time_iso_string(vm, args)
diff --git a/crates/oxide_vm/src/bindings/bind_temporal.rs b/crates/oxide_vm/src/bindings/bind_temporal.rs
index bcc8f900..9eb398e6 100644
--- a/crates/oxide_vm/src/bindings/bind_temporal.rs
+++ b/crates/oxide_vm/src/bindings/bind_temporal.rs
@@ -510,6 +510,16 @@ pub fn bind_temporal(core: &Arc<KernelCore>, session: &KernelSession, global: &m
                 oxide_builtins::temporal::plain_date_time_to_json::<crate::vm::Vm> as *const (),
                 0,
             ),
+            (
+                "add",
+                oxide_builtins::temporal::plain_date_time_add::<crate::vm::Vm> as *const (),
+                1,
+            ),
+            (
+                "subtract",
+                oxide_builtins::temporal::plain_date_time_subtract::<crate::vm::Vm> as *const (),
+                1,
+            ),
         ],
     );
     bind_well_known_data_property(
diff --git a/crates/oxide_vm/tests/builtins_temporal_tests.rs b/crates/oxide_vm/tests/builtins_temporal_tests.rs
index b245e6bf..77c518b2 100644
--- a/crates/oxide_vm/tests/builtins_temporal_tests.rs
+++ b/crates/oxide_vm/tests/builtins_temporal_tests.rs
@@ -821,3 +821,26 @@ fn zdt_subclass_compare_debug() {
     .unwrap();
     assert_eq!(str_val(&vm, r), "number:-1");
 }
+
+#[test]
+fn plain_date_time_add_balances_months_days_and_time() {
+    let mut vm = Vm::new();
+    let r = eval(
+        &mut vm,
+        "const a = Temporal.PlainDateTime.from('1997-12-01T12:34');
+         const b = a.add(new Temporal.Duration(3, 6, 0, 17));
+         const c = a.add(new Temporal.Duration(0, 1, 0, 0, 36));
+         const d = a.subtract(new Temporal.Duration(0, 0, 0, 1));
+         const constrained = new Temporal.PlainDateTime(2020, 1, 31, 15, 0).add({ months: 1 });
+         const rejected = (() => { try {
+           new Temporal.PlainDateTime(2020, 1, 31, 15, 0).add({ months: 1 }, { overflow: 'reject' });
+           return false;
+         } catch (e) { return e instanceof RangeError; } })();
+         [b.year, b.month, b.day, b.hour, b.minute, b.second,
+          c.day, c.hour,
+          d.year, d.month, d.day,
+          constrained.month, constrained.day, rejected].join(':')",
+    )
+    .unwrap();
+    assert_eq!(str_val(&vm, r), "2001:6:18:12:34:0:3:0:1997:11:30:2:29:true");
+}