diff --git a/bsp/simulator/SConstruct b/bsp/simulator/SConstruct
index 2ecec9ef2..b75c4b115 100644
--- a/bsp/simulator/SConstruct
+++ b/bsp/simulator/SConstruct
@@ -9,8 +9,13 @@ else:
 
 # if you want use the rtgui in the svn (in google code), you should
 # comment the following line
-RTT_RTGUI = os.path.normpath('F:/Project/git/rt-gui')
-#RTT_RTGUI =''
+if os.getenv('RTT_RTGUI'):
+    RTT_RTGUI = os.getenv('RTT_RTGUI')
+else:
+    # set the rtgui root directory by hand
+    # empty string means use the RTGUI in svn
+    #RTT_RTGUI = os.path.normpath('F:/Project/git/rt-gui')
+    RTT_RTGUI =''
 
 sys.path = sys.path + [os.path.join(RTT_ROOT, 'tools')]
 from building import *
@@ -52,14 +57,8 @@ env['LIBS']=libs
 env['CPPDEFINES']=definitions
 
 # prepare building environment
-if RTT_RTGUI:
-    objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=False, remove_components=['rtgui'])
-    objs += SConscript(os.path.join(RTT_RTGUI + '/components/rtgui', 'SConscript'),
-					   variant_dir='build/components/rtgui',
-					   duplicate=0)
-else:
-    objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=False)
 
+objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=False, remove_components=['rtgui'])
 if GetDepend('RT_USING_RTGUI'):
     sdl_lib = ['SDL', 'SDLmain']
     sdl_lib_path = os.path.normpath('SDL/lib/x86')
@@ -69,9 +68,15 @@ if GetDepend('RT_USING_RTGUI'):
     env.Append(CPPPATH=sdl_include_path)
 
     if RTT_RTGUI:
+        objs += SConscript(os.path.join(RTT_RTGUI + '/components/rtgui', 'SConscript'),
+						   variant_dir='build/components/rtgui',
+						   duplicate=0)
         objs = objs + SConscript(RTT_RTGUI+'/demo/examples/SConscript', 
 				variant_dir='build/examples/gui', duplicate=0)
     else:
+        objs += SConscript(os.path.join(RTT_ROOT + '/components/rtgui', 'SConscript'),
+						   variant_dir='build/components/rtgui',
+						   duplicate=0)
         objs = objs + SConscript(RTT_ROOT + '/examples/gui/SConscript', 
 				variant_dir='build/examples/gui', duplicate=0)