Abstract: Based on the generalized non-Newton constitutive equation, a finite volume method was used to simulate the water-assisted injection molding of short-glass-fiber-reinforced polypropylene (PP) under the different water injection pressure control modes. The simulation results indicated that the change of water injection pressure control mode had a certain influence on the residual wall thickness and eccentricity rate of the water-assisted injection molded parts. The residual wall thickness between different groups was similar and the eccentricity rate was larger when using the polyline control mode. The residual wall thickness also became more uniform in the same group. Using the stepwise control method, the residual wall thickness was not similar under different groups, and the eccentricity rate was small. The residual wall thickness also changed significantly under the same group.