Water-projectile-assisted injection molding (W-PAIM) process, an innovative processing technology in which the pressurized water is utilized to drive a projectile to penetrate in the core melt, can be used to manufacture hollow plastic pipes. The residual wall thickness of W-PAIM pipes with curved sections was investigated via experiments and numerical simulations. The experiments results of WAIM and W-PAIM pipes were compared and it is found that the residual wall thickness of W-PAIM pipes is much thinner. The main influencing factors of the residual wall thickness of W-PAIM pipes are the section size of the projectile used and the squeezing of the pressurized water on the melt at the end of the projectile during the penetration. Experimental study and numerical simulation on the residual wall thickness of the W-PAIM pipes with curved sections of the same bend radius and different deflection angle were carried out. A thinner inner wall thickness and a thicker outer wall thickness are found at the curved sections and the wall thickness difference increases as the deflection angle increases. The thickness at the curved sections of different radius and the same deflection angle of 90° were investigated via experiment and simulations. It is found that the wall thickness difference decrease as the bend radius increases. The results can be explained by the characteristics of the pressure distribution and the velocity distribution at the bend segments which are discovered by the pressure field and velocity field from the numerical simulation results.