Abstract: The numerical simulation of the cross abnormity fibre with the extrusion process was researched based on polyflow software in this paper. The simulation results indicate: The reorder of the extrusive velocity and the extrusion swell of the polymer melt are arised after the spinneret. And the surface tension is the main factor of the transformation of the fibre section. So the tension factor to the fibre spinnability should be considered to the design of the spinneret. To obtain the accurate section of abnormity fibre, the numerical simulation of the antidromic extrusion process of polymer melt should be accomplishec before the design of spinneret. The research results will have the important effect to the exploiture of abnormity fibre.