The motion characteristics of the fluid in the pulper cavity were obtained by studying its internal area. The interaction between the rotating and stationary areas was handled using a multi-reference frame model in FLUENT software. Fluid simulation analysis was conducted on the wall surface with and without feeding paddle, as well as with different numbers of spoilers (none, one, three, or four), to obtain velocity streamline distribution, turbulent kinetic energy distribution, and cutter surface pressure distribution within the cavity. It’s found that the wall structure with feeding paddle and three spoilers has greatly improved the flow performance of the internal flow field of the pulper.