diff --git a/Cad/FeatureDrivenDrawer.cs b/Cad/FeatureDrivenDrawer.cs
index 6b7cd42..7bfbb07 100644
--- a/Cad/FeatureDrivenDrawer.cs
+++ b/Cad/FeatureDrivenDrawer.cs
@@ -595,9 +595,34 @@ namespace CadParamPluging.Cad
         /// </summary>
         private static void DrawRingSymmetryAxis(DrawingContext ctx, double ox, double oy, double height)
         {
-            // 直接使用“高度标注”的两端点（锻件外轮廓的上下边），不做上下延长，避免越过图框上边界。
-            var y0 = oy;
-            var y1 = oy + height;
+            const double extend = 5.0;       // 中心线在轮廓上下各延长一点（与其它中心线的延长量保持一致）
+            const double frameMargin = 5.0;  // 避免越过图框边界
+
+            var y0 = oy - extend;
+            var y1 = oy + height + extend;
+
+            // 若能检测到白色外框，则把中心线端点夹在图框内（留出少量安全边距）。
+            try
+            {
+                var frameExtents = TemplateDrawingService.ComputeWhiteFrameExtents(ctx?.Ctx);
+                if (frameExtents.HasValue)
+                {
+                    var frame = frameExtents.Value;
+                    y0 = Math.Max(y0, frame.MinPoint.Y + frameMargin);
+                    y1 = Math.Min(y1, frame.MaxPoint.Y - frameMargin);
+                }
+            }
+            catch
+            {
+                // ignore
+            }
+
+            // 极端情况下（图框过小/检测异常导致端点反转）退回到原始高度。
+            if (y1 <= y0)
+            {
+                y0 = oy;
+                y1 = oy + height;
+            }
 
             var line = new Line(new Point3d(ox, y0, 0), new Point3d(ox, y1, 0));
             ctx.Style?.Apply(line, DrawingStyleManager.Role.Centerline);