diff --git a/entry/src/main/ets/pages/Index.ets b/entry/src/main/ets/pages/Index.ets
index 6934b1c..b658836 100644
--- a/entry/src/main/ets/pages/Index.ets
+++ b/entry/src/main/ets/pages/Index.ets
@@ -89,6 +89,10 @@ struct Index {
    *  连 itemGenerator 都不重新执行 ⇒ 内层永远拿到旧的 cells（hasEvent 全 false）。
    *  只改内层 key 是没用的，必须让外层 key 变。 */
   @State monthDataVersion: number = 0;
+  /** ⭐ 用户**主动选中**的日号（1~31）。翻月时用它算目标日，
+   *  避免"1/31 → 2/28 → 3/28"这种日号被永久钳死的问题：
+   *  有了它，2 月显示 28 号，翻到 3 月能回到 31 号。 */
+  @State preferredDay: number = new Date().getDate();
   @State syncing: boolean = false;
   @State loading: boolean = true;
   @State menuOpen: boolean = false; // 顶部 ≡ 下拉菜单
@@ -633,6 +637,14 @@ struct Index {
     const nm = this.addMonths(this.displayYear, this.displayMonth, delta);
     this.displayYear = nm[0];
     this.displayMonth = nm[1];
+    // ⭐ KEEP_SELECTED_DAY 翻月后必须把选中日**迁到新月份的同一天**。
+    //    原来这里只改 displayMonth、不动 selectedDate，
+    //    导致 selectedDate 还停在上个月 ⇒ 新月份所有格子都匹配不上，
+    //    整个月没有任何一天是选中态（用户看到的"乱跳/没有选中"）。
+    // ⭐ 用 preferredDay（用户原本选的日号）而不是 selectedDate 的日号：
+    //    否则 1/31 → 2/28 之后，再翻月就一直是 28 号，回不到 31。
+    const lastDay: number = new Date(nm[0], nm[1] + 1, 0).getDate();
+    this.selectedDate = new Date(nm[0], nm[1], Math.min(this.preferredDay, lastDay)).getTime();
     this.reloadEvents();
     this.swiperGuard = true;
     this.swiperController.changeIndex(1, false);
@@ -3389,6 +3401,8 @@ struct Index {
     .justifyContent(FlexAlign.Center)
     .onClick(() => {
       this.selectedDate = cell.dateMs;
+      // 用户主动点了某天 ⇒ 记住这个日号，作为后续翻月的基准
+      this.preferredDay = new Date(cell.dateMs).getDate();
       if (!cell.inMonth) {
         const d = new Date(cell.dateMs);
         this.displayYear = d.getFullYear();
diff --git a/scripts/test-month-swipe-selection.js b/scripts/test-month-swipe-selection.js
new file mode 100644
index 0000000..8c378ed
--- /dev/null
+++ b/scripts/test-month-swipe-selection.js
@@ -0,0 +1,65 @@
+// 验证 preferredDay 机制消除日号漂移
+function addMonths(y, m, delta) {
+  let mm = m + delta, yy = y;
+  while (mm < 0) { mm += 12; yy--; }
+  while (mm > 11) { mm -= 12; yy++; }
+  return [yy, mm];
+}
+function migrate(preferredDay, y, m, delta) {
+  const nm = addMonths(y, m, delta);
+  const lastDay = new Date(nm[0], nm[1] + 1, 0).getDate();
+  return { ms: new Date(nm[0], nm[1], Math.min(preferredDay, lastDay)).getTime(), y: nm[0], m: nm[1] };
+}
+function fmt(ms) {
+  const d = new Date(ms);
+  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
+}
+
+let pass = 0, fail = 0;
+function ok(name, cond, extra) {
+  if (cond) { console.log('  ✅', name); pass++; }
+  else { console.log('  ❌', name, extra); fail++; }
+}
+
+// 1. 偏好 31 号：1/31 → 2/28 → 3/31（回到 31！）
+let pref = 31, y = 2026, m = 0, cur = new Date(2026, 0, 31).getTime(), log = [];
+for (let i = 0; i < 4; i++) {
+  const r = migrate(pref, y, m, 1);
+  cur = r.ms; y = r.y; m = r.m;
+  log.push(fmt(cur));
+}
+console.log('  偏好31号连续翻月:', log.join(' → '));
+ok('1/31→2/28→3/31→4/30（月底语义保留）',
+  log[0] === '2026-02-28' && log[1] === '2026-03-31' && log[2] === '2026-04-30',
+  log.join(','));
+ok('第4次翻到5月回到31', log[3] === '2026-05-31', log[3]);
+
+// 2. 偏好 15 号：一直稳定
+pref = 15; y = 2026; m = 0; log = [];
+for (let i = 0; i < 6; i++) {
+  const r = migrate(pref, y, m, 1);
+  y = r.y; m = r.m; log.push(fmt(r.ms));
+}
+ok('偏好15号稳定', log.every(s => s.endsWith('-15')), log.join(','));
+
+// 3. 用户点 2/28 后偏好变 28，翻到 3 月应是 28 号
+pref = 28; y = 2026; m = 1;
+let r = migrate(pref, y, m, 1);
+ok('点过28号后翻月为3/28', fmt(r.ms) === '2026-03-28', fmt(r.ms));
+
+// 4. 闰年偏好 31
+pref = 31; y = 2028; m = 0;
+r = migrate(pref, y, m, 1);
+ok('闰年 1/31 → 2/29', fmt(r.ms) === '2028-02-29', fmt(r.ms));
+r = migrate(pref, 2028, 1, 1);
+ok('闰年 2/29 → 3/31', fmt(r.ms) === '2028-03-31', fmt(r.ms));
+
+// 5. 往前翻同样保留
+pref = 31; y = 2026; m = 2;  // 3月
+r = migrate(pref, y, m, -1);
+ok('3/31 上月 → 2/28', fmt(r.ms) === '2026-02-28', fmt(r.ms));
+r = migrate(pref, 2026, 1, -1);
+ok('2/28 再上月 → 1/31', fmt(r.ms) === '2026-01-31', fmt(r.ms));
+
+console.log(`\n结果：通过 ${pass}，失败 ${fail}`);
+process.exit(fail === 0 ? 0 : 1);
\ No newline at end of file