diff --git a/app/models.py b/app/models.py
index b593dfa..1dc6b54 100644
--- a/app/models.py
+++ b/app/models.py
@@ -173,6 +173,7 @@ class ChartInput(BaseModel):
     taskId: str | None = None
     metricId: str | None = None
     days: Annotated[int, Field(ge=7, le=365)] = 30
+    yMax: Annotated[int | None, Field(ge=1)] = None
 
 
 class ChartUpdate(ChartInput):
diff --git a/app/static/app.js b/app/static/app.js
index 1ab70e8..b1d8308 100644
--- a/app/static/app.js
+++ b/app/static/app.js
@@ -109,20 +109,32 @@ function periodText(task) { const metrics = task.metrics || []; return [...new S
 function summaryFor(taskId) { return state.summary?.tasks?.[taskId] || null; }
 function metricSummary(taskId, metricId) { return summaryFor(taskId)?.metrics?.find((metric) => metric.metricId === metricId) || null; }
 
+function niceCeil(value) {
+  if (!(value > 0)) return 1;
+  const magnitude = Math.pow(10, Math.floor(Math.log10(value)));
+  const steps = [1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10];
+  for (const step of steps) {
+    const candidate = step * magnitude;
+    if (value <= candidate) return Number(candidate.toFixed(6));
+  }
+  return magnitude * 10;
+}
+
 function renderChartSvg(chart) {
   const points = chart.data?.points || [];
   if (!points.length || points.every((point) => Number(point.value) === 0)) return `<div class="chart-empty">暂无数据</div>`;
-  const width = 600, height = 200, pad = { left: 34, right: 12, top: 14, bottom: 30 };
-  const max = Math.max(...points.map((point) => Number(point.value) || 0), 1);
+  const width = 600, height = 200, pad = { left: 34, right: 12, top: 16, bottom: 30 };
+  const dataMax = Math.max(...points.map((point) => Number(point.value) || 0), 1);
+  const scaleMax = chart.yMax ? Math.max(Number(chart.yMax), dataMax) : niceCeil(dataMax * 1.25);
   const x = (index) => pad.left + (points.length === 1 ? 0 : index * (width - pad.left - pad.right) / (points.length - 1));
-  const y = (value) => pad.top + (height - pad.top - pad.bottom) * (1 - value / max);
+  const y = (value) => pad.top + (height - pad.top - pad.bottom) * (1 - value / scaleMax);
   const coords = points.map((point, index) => `${x(index).toFixed(1)},${y(Number(point.value) || 0).toFixed(1)}`).join(" ");
   const areaPath = `M ${pad.left.toFixed(1)} ${y(0).toFixed(1)} L ${coords.replace(/ /g, " L ")} L ${x(points.length - 1).toFixed(1)} ${y(0).toFixed(1)} Z`;
   const labels = [points[0], points[Math.floor((points.length - 1) / 2)], points[points.length - 1]].filter((point, index, list) => point && list.findIndex((item) => item.date === point.date) === index).map((point) => {
     const index = points.indexOf(point); return `<text x="${x(index)}" y="${height - 7}" text-anchor="middle">${escapeHtml(point.date.slice(5))}</text>`;
   }).join("");
   const circles = points.map((point, index) => `<circle cx="${x(index).toFixed(1)}" cy="${y(Number(point.value) || 0).toFixed(1)}" r="2.2"/>`).join("");
-  return `<svg class="chart-svg" viewBox="0 0 ${width} ${height}" preserveAspectRatio="none" role="img" aria-label="${escapeHtml(chart.title)}"><line class="chart-guide" x1="${pad.left}" y1="${y(0)}" x2="${width - pad.right}" y2="${y(0)}"/><line class="chart-guide" x1="${pad.left}" y1="${y(max)}" x2="${width - pad.right}" y2="${y(max)}"/><text class="chart-max" x="4" y="${y(max) + 4}">${max}</text><path class="chart-area" d="${areaPath}"/><polyline points="${coords}"/><g class="chart-points">${circles}</g><g class="chart-labels">${labels}</g></svg>`;
+  return `<svg class="chart-svg" viewBox="0 0 ${width} ${height}" preserveAspectRatio="none" role="img" aria-label="${escapeHtml(chart.title)}"><line class="chart-guide" x1="${pad.left}" y1="${y(0)}" x2="${width - pad.right}" y2="${y(0)}"/><line class="chart-guide" x1="${pad.left}" y1="${y(scaleMax)}" x2="${width - pad.right}" y2="${y(scaleMax)}"/><text class="chart-max" x="4" y="${y(scaleMax) + 4}">${scaleMax}</text><path class="chart-area" d="${areaPath}"/><polyline points="${coords}"/><g class="chart-points">${circles}</g><g class="chart-labels">${labels}</g></svg>`;
 }
 
 function renderReviewCharts() {
@@ -147,7 +159,7 @@ function openChartDialog(chart = null) {
   state.editingChartId = chart?.chartId || null;
   const form = $("#chartForm"); form.reset(); $("#chartDialogTitle").textContent = chart ? "编辑图表" : "添加图表";
   $("#chartTaskSelect").innerHTML = `<option value="">全部任务</option>${state.tasks.map((task) => `<option value="${escapeHtml(task.taskId)}">${escapeHtml(task.name)}</option>`).join("")}`;
-  form.title.value = chart?.title || ""; form.days.value = chart?.days || 30; $("#chartTaskSelect").value = chart?.taskId || ""; fillChartMetrics($("#chartTaskSelect").value, chart?.metricId || ""); $("#chartDialog").showModal();
+  form.title.value = chart?.title || ""; form.days.value = chart?.days || 30; form.yMax.value = chart?.yMax || ""; $("#chartTaskSelect").value = chart?.taskId || ""; fillChartMetrics($("#chartTaskSelect").value, chart?.metricId || ""); $("#chartDialog").showModal();
 }
 
 function bindReviewCharts() {
@@ -565,7 +577,7 @@ $("#chartTaskSelect").addEventListener("change", (event) => fillChartMetrics(eve
 $("#chartForm").addEventListener("submit", async (event) => {
   event.preventDefault();
   const form = event.currentTarget;
-  const payload = { title: form.title.value, taskId: form.taskId.value || null, metricId: form.metricId.value || null, days: Number(form.days.value) };
+  const payload = { title: form.title.value, taskId: form.taskId.value || null, metricId: form.metricId.value || null, days: Number(form.days.value), yMax: form.yMax.value ? Number(form.yMax.value) : null };
   try {
     const editing = state.editingChartId ? state.charts.find((chart) => chart.chartId === state.editingChartId) : null;
     if (editing) payload.expectedVersion = editing.version;
diff --git a/app/static/index.html b/app/static/index.html
index 0011f12..6523183 100644
--- a/app/static/index.html
+++ b/app/static/index.html
@@ -70,6 +70,7 @@
         <label>任务<select name="taskId" id="chartTaskSelect"><option value="">全部任务</option></select></label>
         <label>指标<select name="metricId" id="chartMetricSelect"><option value="">完成数</option></select></label>
         <label>天数<input name="days" type="number" min="7" max="365" value="30" required></label>
+        <label>纵轴上限<input name="yMax" type="number" min="1" placeholder="自动"></label>
       </div>
       <div class="dialog-actions"><button class="button" id="cancelChartButton" type="button">取消</button><button class="button primary" type="submit">保存图表</button></div>
     </form>
diff --git a/tests/test_charts.py b/tests/test_charts.py
index 978fff4..23cefe4 100644
--- a/tests/test_charts.py
+++ b/tests/test_charts.py
@@ -29,6 +29,14 @@ def test_chart_crud_and_conflict(tmp_path):
     assert repo.delete_chart(chart["chartId"])["deleted"] is True
 
 
+def test_chart_yMax_roundtrip(tmp_path):
+    repo = JsonRepository(tmp_path)
+    bounded = repo.create_chart(ChartInput(title="带上限", yMax=10))
+    assert repo.get_chart(bounded["chartId"])["yMax"] == 10
+    auto = repo.create_chart(ChartInput(title="自动"))
+    assert repo.get_chart(auto["chartId"])["yMax"] is None
+
+
 def test_chart_data_modes_and_continuous_points(tmp_path):
     repo = JsonRepository(tmp_path)
     task = _task(repo)