Using Solidworks 3D modeling software to establish the model of Tian-Shaped plastics profile extrusion die. One-quarter part of the Die was divided into ANSYS grid. The melt of poly lactic acid was used as fluid at 190 ℃ in Polyflow simulation analysis. The flow field simulation results of the normal die and the design of the inverse extrusion die were obtained. The flow field and extrusion shape of seven cross sections were compared and analyzed. And the flow chart of typical sections was compared in depth. The results showed that the flow velocity distribution in the die was more uniform. The flow rate in the die increased slightly and then decreased to a stable value and the shape of final section was composite requirement.