diff --git a/miniapp/pages/index/index.js b/miniapp/pages/index/index.js
index 689d992..fc30e3a 100644
--- a/miniapp/pages/index/index.js
+++ b/miniapp/pages/index/index.js
@@ -359,6 +359,16 @@ function getSvgLabelPlacement(layout, isSource, labelPositionMode) {
   };
 }
 
+/**
+ * 标签纵坐标限制在画布安全区内，避免上下溢出。
+ */
+function getClampedLabelY(nodeY, nodeHeight, canvasHeight, chartPadding) {
+  const rawY = nodeY + getNodeLabelCenterY(nodeHeight);
+  const safeTop = Math.max(0, chartPadding + 6);
+  const safeBottom = Math.max(safeTop, canvasHeight - chartPadding - 6);
+  return Math.min(safeBottom, Math.max(safeTop, rawY));
+}
+
 /**
  * 统一生成桑基图布局数据，供 canvas 渲染与 SVG 导出共用。
  */
@@ -368,7 +378,9 @@ function buildSankeyLayout(links, width, height, renderOptions) {
   }
 
   const nodeGap = clampNumber(renderOptions && renderOptions.nodeGap, 0, 60, 8);
-  const padding = clampNumber(renderOptions && renderOptions.chartPadding, 0, 120, 16);
+  const rawPadding = clampNumber(renderOptions && renderOptions.chartPadding, 0, 120, 16);
+  // 纵向限制：padding 不能超过可视高度的一半，避免节点整体被挤出画布。
+  const padding = Math.min(rawPadding, Math.max(0, height / 2 - 4));
   const targetAlignMode = (renderOptions && renderOptions.targetAlignMode) || 'between';
   const nodeWidth = 10;
   const leftX = padding;
@@ -399,7 +411,7 @@ function buildSankeyLayout(links, width, height, renderOptions) {
   }
 
   const sourceGapCount = Math.max(0, sourceNames.length - 1);
-  const sourceContentHeight = Math.max(10, height - padding * 2 - sourceGapCount * nodeGap);
+  const sourceContentHeight = Math.max(0, height - padding * 2 - sourceGapCount * nodeGap);
   const sourceUnitHeight = sourceContentHeight / totalValue;
   const sourceTotalNodeHeight = totalValue * sourceUnitHeight;
   const sourceSpanHeight = sourceTotalNodeHeight + sourceGapCount * nodeGap;
@@ -407,7 +419,7 @@ function buildSankeyLayout(links, width, height, renderOptions) {
   const sourcePos = {};
   let sourceCursorY = padding;
   sourceNames.forEach((name) => {
-    const nodeHeight = Math.max(2, sourceValueMap[name] * sourceUnitHeight);
+    const nodeHeight = sourceValueMap[name] * sourceUnitHeight;
     sourcePos[name] = { y: sourceCursorY, h: nodeHeight };
     sourceCursorY += nodeHeight + nodeGap;
   });
@@ -436,7 +448,7 @@ function buildSankeyLayout(links, width, height, renderOptions) {
   const targetPos = {};
   let targetCursorY = targetStartY;
   targetNames.forEach((name) => {
-    const nodeHeight = Math.max(2, targetValueMap[name] * targetUnitHeight);
+    const nodeHeight = targetValueMap[name] * targetUnitHeight;
     targetPos[name] = { y: targetCursorY, h: nodeHeight };
     targetCursorY += nodeHeight + targetGap;
   });
@@ -458,7 +470,10 @@ function buildSankeyLayout(links, width, height, renderOptions) {
       return;
     }
 
-    const linkHeight = Math.max(1, Number(link.value || 0) * sourceUnitHeight);
+    const linkHeight = Number(link.value || 0) * sourceUnitHeight;
+    if (linkHeight <= 0) {
+      return;
+    }
     const sy = sourceNode.y + sourceOffset[link.source] + linkHeight / 2;
     const ty = targetNode.y + targetOffset[link.target] + linkHeight / 2;
     sourceOffset[link.source] += linkHeight;
@@ -539,7 +554,12 @@ function buildSankeySvgText(links, width, height, renderOptions) {
     const colorIndex = Number.isFinite(layout.nodeColorIndexMap[name])
       ? layout.nodeColorIndexMap[name]
       : index;
-    const textY = node.y + getNodeLabelCenterY(node.h);
+    const textY = getClampedLabelY(
+      node.y,
+      node.h,
+      height,
+      clampNumber(renderOptions && renderOptions.chartPadding, 0, 120, 16)
+    );
     const textPlacement = getSvgLabelPlacement(layout, true, labelPositionMode);
     segments.push(
       `<rect x="${formatSvgNumber(layout.leftX)}" y="${formatSvgNumber(node.y)}" width="${formatSvgNumber(
@@ -558,7 +578,12 @@ function buildSankeySvgText(links, width, height, renderOptions) {
     const colorIndex = Number.isFinite(layout.nodeColorIndexMap[name])
       ? layout.nodeColorIndexMap[name]
       : index;
-    const textY = node.y + getNodeLabelCenterY(node.h);
+    const textY = getClampedLabelY(
+      node.y,
+      node.h,
+      height,
+      clampNumber(renderOptions && renderOptions.chartPadding, 0, 120, 16)
+    );
     const textPlacement = getSvgLabelPlacement(layout, false, labelPositionMode);
     segments.push(
       `<rect x="${formatSvgNumber(layout.rightX)}" y="${formatSvgNumber(node.y)}" width="${formatSvgNumber(
@@ -1261,13 +1286,14 @@ Page({
         const colorIndex = Number.isFinite(layout.nodeColorIndexMap[name])
           ? layout.nodeColorIndexMap[name]
           : index;
+        const textY = getClampedLabelY(node.y, node.h, height, this.data.chartPadding);
         ctx.setFillStyle(getNodeColor(colorIndex, themeColors));
         ctx.fillRect(layout.leftX, node.y, layout.nodeWidth, node.h);
         ctx.setFillStyle('#4e5969');
         ctx.setFontSize(10);
         ctx.setTextAlign(labelPlacement.textAlign);
         ctx.setTextBaseline('middle');
-        ctx.fillText(name, labelPlacement.x, node.y + getNodeLabelCenterY(node.h));
+        ctx.fillText(name, labelPlacement.x, textY);
       });
 
       layout.targetNames.forEach((name, index) => {
@@ -1276,13 +1302,14 @@ Page({
         const colorIndex = Number.isFinite(layout.nodeColorIndexMap[name])
           ? layout.nodeColorIndexMap[name]
           : index;
+        const textY = getClampedLabelY(node.y, node.h, height, this.data.chartPadding);
         ctx.setFillStyle(getNodeColor(colorIndex, themeColors));
         ctx.fillRect(layout.rightX, node.y, layout.nodeWidth, node.h);
         ctx.setFillStyle('#4e5969');
         ctx.setFontSize(10);
         ctx.setTextAlign(labelPlacement.textAlign);
         ctx.setTextBaseline('middle');
-        ctx.fillText(name, labelPlacement.x, node.y + getNodeLabelCenterY(node.h));
+        ctx.fillText(name, labelPlacement.x, textY);
       });
 
       ctx.draw();
diff --git a/miniapp/pages/index/index.wxss b/miniapp/pages/index/index.wxss
index 6e1e0f7..5d7c0cf 100644
--- a/miniapp/pages/index/index.wxss
+++ b/miniapp/pages/index/index.wxss
@@ -234,7 +234,7 @@
 .preview-canvas {
   margin-top: 3px;
   width: 100%;
-  height: auto;
+  height: 0;
   flex: 1;
   min-height: 120px;
   border-radius: 4px;