diff --git a/src/IFoxCAD.Cad/ExtensionMethod/IsOnLine b/src/IFoxCAD.Cad/ExtensionMethod/IsOnLine
new file mode 100644
index 0000000000000000000000000000000000000000..61bb01ec53336036238d8b463f4aeaaaf8be5e59
--- /dev/null
+++ b/src/IFoxCAD.Cad/ExtensionMethod/IsOnLine
@@ -0,0 +1,96 @@
+    /// <summary>
+    /// 判断点与另外两点的位置关系
+    /// </summary>
+    /// <param name="Point">基点</param>
+    /// <param name="StartPoint">起点</param>
+    /// <param name="EndPoint">终点</param>
+    /// <param name="dTol">容差</param>
+    /// <returns>枚举类型</returns>
+    public static PointOnlineType IsOnLine(this Point3d Point, Point3d StartPoint, Point3d EndPoint, double dTol)
+    {
+        //以点Point为坐标系Y轴与直线的交点距离，正值则点在直线之上，负值则点在直线之下，零则在直线上
+        var dd = (Point.X - StartPoint.X) * (StartPoint.Y - EndPoint.Y) - (Point.Y - StartPoint.Y) * (EndPoint.X - StartPoint.X);
+        //点StartPoint与点EndPoint的直线距离
+        var d12 = Math.Abs(StartPoint.DistanceTo(EndPoint));
+        //点Point与点StartPoint的直线距离
+        var d01 = Math.Abs(Point.DistanceTo(StartPoint));
+        //点Point与点EndPoint的直线距离
+        var d02 = Math.Abs(Point.DistanceTo(EndPoint));
+        if (dd >0)
+        {
+            return PointOnlineType.OnLineUp;
+        }
+        else if (dd < 0)
+        {
+            return PointOnlineType.OnLineDown;
+        }
+        else 
+        {
+            //点Point在直线起点段的延长线上
+            if (d02.Equals(d01 + d12))
+            {
+                //点Point在直线起点段的延长线上且小于等于误差长度
+                if (d01 <= dTol)
+                {
+                    return PointOnlineType.ExtendLineStartPointIn;
+                }
+                else
+                {
+                    return PointOnlineType.ExtendLineStartPointOut;
+                }
+            }
+            //点Point在直线终点段的延长线上
+            else if (d01.Equals(d02 + d12))
+            {                
+                //点Point在直线终点段的延长线上且小于等于误差长度
+                if (d02 <= dTol)
+                {
+                    return PointOnlineType.ExtendLineEndPointIn;
+                }
+                else
+                {
+                    return PointOnlineType.ExtendLineEndPointOut;
+                }
+            }
+            //点Point在直线两点之间
+            else
+            {
+                return PointOnlineType.OnLine;
+            }
+        }
+    }
+
+    /// <summary>
+/// 点与直线关系类型枚举
+/// </summary>
+public enum PointOnlineType
+{
+    /// <summary>
+    /// 直线上两点之间
+    /// </summary>
+    OnLine,
+    /// <summary>
+    /// 直线延长线起点误差距离之内
+    /// </summary>
+    ExtendLineStartPointIn,
+    /// <summary>
+    /// 直线延长线起点误差距离之外
+    /// </summary>
+    ExtendLineStartPointOut,
+    /// <summary>
+    /// 直线延长线终点误差距离之内
+    /// </summary>
+    ExtendLineEndPointIn,
+    /// <summary>
+    /// 直线延长线终点误差距离之外
+    /// </summary>
+    ExtendLineEndPointOut,
+    /// <summary>
+    /// 直线之上
+    /// </summary>
+    OnLineUp,
+    /// <summary>
+    /// 直线之下
+    /// </summary>
+    OnLineDown,
+}
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