diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index 74b4035957..3142d491a3 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -3798,6 +3798,11 @@ bool GCode::needs_retraction(const Polyline &travel, ExtrusionRole role)
         return false;
     }
 
+    //BBS: force to retract when leave from external perimeter for a long travel
+    //Better way is judging whether the travel move direction is same with last extrusion move.
+    if (is_perimeter(m_last_processor_extrusion_role) && m_last_processor_extrusion_role != erPerimeter)
+        return true;
+
     if (role == erSupportMaterial || role == erSupportTransition) {
         const SupportLayer* support_layer = dynamic_cast<const SupportLayer*>(m_layer);
         //FIXME support_layer->support_islands.contains should use some search structure!