Based on the limitation of the eccentric twin screw extruder's own structure, a new type of eccentric three screw extruder was designed. Polyflow software was used to analyze the pressure field, shree velocity field, velocity vector field, mixing index, separation scale, average mixing efficiency, logarithmic stretching and other parameters. The flow and mixing mechanism of the eccentric tri?screw extruder were studied and compared with that of the eccentric twin?screw extruder. The results show that under the same conditions, the stretching and folding effect of the eccentric three?screw extruder is better, and the mixing efficiency is higher than that of the eccentric twin?screw extruder, which provides a theoretical basis for further exploring the chaotic mixing mechanism and optimizing the eccentric multi?screw extruder.