Thanks Ralf .
Yes I dragged ,but I guess it may be something related with pixel or scale things which made it failed .
Below shows error tips after I dragged .
the size of my layout is 402merters *233meters .
Do you have any ideas ?
Well ,this is a DWG file created using Auto CAD 2014 .And there are a lot of setting inside it ,like layers, color .So I am not sure if these will have a influence .
And I tried to draw a new one which size is much smaller and simpler than the layout ,and dragged it to add ,it worked .
When I build simulation model for each section seperately ,the size of layout and the size of file became smaller then it worked .So I guess we may know the reason now .
Any way ,thanks Ralf .