In order to investigate the influence of geometric parameters of screw extruder on the shear rate of polymer melt, the flow morphology and mixing mechanism of polymer material melt in twin-screw extruder were deeply explored. This study focuses on polymer melt materials and takes the industrial prototype of a fully meshed co rotating twin-screw extruder as the object. Combined with POLYLOW software modeling, three-dimensional isothermal flow field numerical simulation of polymer melt materials is carried out, and the fluid velocity field and other field quantities of polymer melt materials are solved; Then, the POLYSTAT post-processing software was used to introduce concepts such as cumulative maximum shear rate distribution to evaluate the dispersion and mixing ability of polymer melt materials; Finally, the laminar shear theory is applied to calculate the viscous shear heat generation of polymer melt materials and compared with actual experimental data. The experimental results show that the change in pitch has little effect on the mixing index and the fluid motion mode; As the pitch increases, the maximum mixing index slightly increases, but the overall dispersion and mixing ability of the screw shows a weakening trend; Small pitch is beneficial for improving the distribution mixing ability; As the pitch increases, the average mixing efficiency shows an increasing trend, and a larger pitch is beneficial for improving the mixing efficiency. Research has shown that the geometric parameters of screw extruders have a significant impact on the shear rate and mixing effect of polymer melts, providing a theoretical basis for optimizing extruder design.