diff --git a/frontend/static/css/display.css b/frontend/static/css/display.css
index 9742bf0..957d7e5 100644
--- a/frontend/static/css/display.css
+++ b/frontend/static/css/display.css
@@ -865,3 +865,9 @@ html, body {
 .cd-item .cd-remain.overdue {
   color: var(--accent-red);
 }
+/* ── Count-up timer (正计时) ──────────────── */
+.countup-section { margin-top: clamp(8px, 1.5vh, 18px); }
+.countup-label { font-size: clamp(12px, 1.6vw, 18px); color: var(--text-dim); margin-bottom: clamp(2px, 0.4vh, 8px); }
+#countup-value { font-size: clamp(24px, 5vw, 64px); margin-bottom: 0; }
+.countup-btns { display: flex; gap: clamp(10px, 1.5vw, 20px); margin-top: clamp(8px, 1.2vh, 16px); }
+.countup-btns .pomo-btn { padding: clamp(6px, 1vh, 12px) clamp(20px, 3vw, 44px); }
diff --git a/frontend/static/js/display.js b/frontend/static/js/display.js
index a96dc38..49e34f7 100644
--- a/frontend/static/js/display.js
+++ b/frontend/static/js/display.js
@@ -36,6 +36,7 @@
     _cdModalMode: false, // true = countdown modal, false = alarm modal
     _editingCountdown: null,
     timezone: 'Asia/Shanghai', // 账户独立时区（来自 /api/display/state）
+    countUp: { status: 'idle', startedAtMs: null, baseSec: 0, frozenSec: 0 },
   };
 
   // ─── DOM refs ─────────────────────────────
@@ -107,6 +108,10 @@
     if (name === 'pomodoro') {
       fetchPomodoro();
     }
+    // Immediately render count-up when switching back to time panel
+    if (name === 'time') {
+      renderCountUpPanel();
+    }
   }
 
   cards.forEach(function (card) {
@@ -1298,6 +1303,108 @@
       n.y + '年' + n.mo + '月' + n.d + '日 星期' + days[n.wd];
   }
 
+  function _calcCountUpElapsed() {
+    var c = state.countUp;
+    if (!c) return 0;
+    if (c.status !== 'running') return c.frozenSec || 0;
+    try {
+      if (c.startedAtMs == null) return c.frozenSec || 0;
+      return (c.baseSec || 0) + Math.floor((Date.now() - c.startedAtMs) / 1000);
+    } catch (_) {
+      return c.frozenSec || 0;
+    }
+  }
+
+  function _formatCountUp(totalSec) {
+    if (typeof totalSec !== 'number' || !isFinite(totalSec) || totalSec < 0) {
+      return '00:00:00';
+    }
+    var h = Math.floor(totalSec / 3600);
+    var m = Math.floor((totalSec % 3600) / 60);
+    var s = totalSec % 60;
+    return _pad2(h) + ':' + _pad2(m) + ':' + _pad2(s);
+  }
+
+  function renderCountUpPanel() {
+    try {
+      var c = state.countUp || {};
+      var el = $('countup-value');
+      if (!el) return;
+      el.textContent = _formatCountUp(_calcCountUpElapsed());
+      var btnStart = $('countup-start');
+      var btnStop = $('countup-stop');
+      var btnReset = $('countup-reset');
+      var running = c.status === 'running';
+      if (btnStart) btnStart.style.display = running ? 'none' : '';
+      if (btnReset) btnReset.style.display = running ? 'none' : '';
+      if (btnStop) btnStop.style.display = running ? '' : 'none';
+    } catch (e) {
+      console.warn('countUp render failed:', e);
+    }
+  }
+
+  function countUpStart() {
+    try {
+      var c = state.countUp;
+      if (c.status === 'running') return;
+      c.baseSec = 0;
+      c.startedAtMs = Date.now();
+      c.status = 'running';
+      renderCountUpPanel();
+    } catch (e) {
+      console.warn('countUp start failed:', e);
+    }
+  }
+
+  function countUpStop() {
+    try {
+      var c = state.countUp;
+      if (c.status !== 'running') return;
+      c.frozenSec = _calcCountUpElapsed();
+      c.startedAtMs = null;
+      c.status = 'idle';
+      renderCountUpPanel();
+    } catch (e) {
+      console.warn('countUp stop failed:', e);
+    }
+  }
+
+  function countUpReset() {
+    try {
+      var c = state.countUp;
+      c.frozenSec = 0;
+      c.startedAtMs = null;
+      c.status = 'idle';
+      renderCountUpPanel();
+    } catch (e) {
+      console.warn('countUp reset failed:', e);
+    }
+  }
+
+  function setupCountUpControls() {
+    var btnStart = $('countup-start');
+    var btnStop = $('countup-stop');
+    var btnReset = $('countup-reset');
+    if (btnStart) {
+      btnStart.addEventListener('click', function (e) {
+        e.stopPropagation();
+        countUpStart();
+      });
+    }
+    if (btnStop) {
+      btnStop.addEventListener('click', function (e) {
+        e.stopPropagation();
+        countUpStop();
+      });
+    }
+    if (btnReset) {
+      btnReset.addEventListener('click', function (e) {
+        e.stopPropagation();
+        countUpReset();
+      });
+    }
+  }
+
   function renderWeatherPanel() {
     var w = state.weather || {};
     if (w.temp === undefined) {
@@ -1621,6 +1728,7 @@
     renderCountdownCard();
     renderPomodoroCard();
     if (state.activePanel === 'time') renderTimePanel();
+    if (state.activePanel === 'time') renderCountUpPanel();
     if (state.activePanel === 'pomodoro') renderPomodoro();
     if (state.activePanel === 'countdown') renderCountdownPanel();
     // Refresh update schedule info every 10s to keep next-update times current
@@ -1648,5 +1756,13 @@
   fetchState();
   connectSSE();
   switchPanel('time');
+  setupCountUpControls();
+  document.addEventListener('visibilitychange', function () {
+    try {
+      if (document.visibilityState === 'visible' && state.activePanel === 'time') {
+        renderCountUpPanel();
+      }
+    } catch (_) {}
+  });
 
 })();
diff --git a/frontend/templates/display.html b/frontend/templates/display.html
index 30f7d5a..3e08594 100644
--- a/frontend/templates/display.html
+++ b/frontend/templates/display.html
@@ -76,6 +76,15 @@
       <h2>时间</h2>
       <div id="detailed-time" class="big-clock">--:--:--</div>
       <div class="date-str" id="date-str"></div>
+      <div class="countup-section">
+        <div class="countup-label">正计时</div>
+        <div id="countup-value" class="big-clock">00:00:00</div>
+        <div class="countup-btns">
+          <button id="countup-start" class="pomo-btn pomo-btn-primary countup-btn">启动</button>
+          <button id="countup-stop" class="pomo-btn pomo-btn-secondary countup-btn" style="display:none;">停止</button>
+          <button id="countup-reset" class="pomo-btn pomo-btn-secondary countup-btn">清零</button>
+        </div>
+      </div>
     </div>
     <div id="panel-weather" class="panel-content">
       <h2>天气</h2>