The SolidWorks 3D modeling software was used to construct the meshing co-rotating twin-screw physical model. By changing the rotational speed of the PLA processed by the screw extruder, the non-isothermal flow analysis was used to carry out the corresponding numerical simulation in the polyflow software. Compare the effect of speed on the processing of PLA. The numerical results show that under non-isothermal conditions, the temperature increases linearly in the direction from the inlet to the outlet, that is, in the extrusion direction. On the Z-axis section, the temperature gradually increases outward in the radial direction. By comparing the flow field analysis at different speeds, it can be concluded that with the increase of rotational speed, there is a large temperature difference in the groove. When the rotational speed reaches 240 r/min, the polymer is partially degraded, which is not conducive to production and processing. The correlation between the shear rate field and the viscosity field is further verified by the comparative analysis.