Thank you !
I'm sorry but I'm a newbie... so... do this Polygon Flag makes my game slower ?
I read from the Manual :
"Only one of the objects involved in a collision should have a polygonal hull. Do not set this flag for moving objects or for animated models."...

and when the flasg Polygon is on, What about the trace_mode of c_trace ? Because I set the polygon but it still like that !

thanks againt !