diff --git a/src/Add-on/Offset.ts b/src/Add-on/Offset.ts
index b627a77a2..a5d562f31 100644
--- a/src/Add-on/Offset.ts
+++ b/src/Add-on/Offset.ts
@@ -33,6 +33,10 @@ export class Command_Offset implements Command
                 let d = cu.GetFistDeriv(cu.GetParamAtPoint(ptClose));//切线。
 
                 let c = toPtVec.cross(d);
+                if (cu instanceof Polyline && cu.EndParam > 1 && cu.Area > 0)
+                {
+                    c.z = (IsPointInPolyLine(cu, p) ? -1 : 1) * Math.sign(cu.Area2);
+                }
 
                 let offCurs = cu.GetOffsetCurves(dis.Value * Math.sign(c.z));
                 offCurs.forEach((offCur) =>
@@ -74,9 +78,9 @@ export class Command_TestOffset implements Command
                     let d = cu.GetFistDeriv(cu.GetParamAtPoint(ptClose));//切线。
                     let c = toPtVec.cross(d);
 
-                    if (cu instanceof Polyline)
+                    if (cu instanceof Polyline && cu.EndParam > 1 && cu.Area > 0)
                     {
-                        c.z = (IsPointInPolyLine(cu, p)) ? 1 : -1;
+                        c.z = (IsPointInPolyLine(cu, p) ? -1 : 1) * Math.sign(cu.Area2);
                     }
 
                     lastpls = cu.GetOffsetCurves(p.distanceTo(cu.GetClosestPointTo(p, !cu.IsClose)) * Math.sign(c.z));