［［Objective ］］ To investigate the influence of material slip on the inner wall of the barrel and the surface of the screw on the extrusion process of the co -rotating twin screw.［［Methods ］］ The 3D model is designed by the relative motion method,and different slip boundary conditions are set and simulated by the finite element method.The relevant physical field data are obtained by simulation analysis,and the volume flow rate is calculated.The physical field of the extrusion process is studied.［［Results ］］ Compared with the non -slip condition,the pressure in the flow channel decreases,the shear rate decreases,and the viscosity increases under the screw slip condition.Under the condition of wall slip,the pressure decreases,the shear rate decreases,and the viscosity increases at the gap between the screw and the barrel.On the contrary,the pressure increases,the shear rate increases,and the viscosity decreases at the screw engagement.The analysis of the volume flow rate in the extrusion process showed that the yield increased by 28% under the screw slip condition,and the yield decreased by 62.5% under the wall slip condition.［［Conclusion ］］ The occurrence of the wall slip phenomenon helps to improve the shear ability of the screw at the screw engagement,and the occurrence of the screw slip phenomenon is beneficial to improve the extrusion yield of the co -directed twin screw.