Abstract: A water-assisted injection molding (WAIM) experiment was carried out for polypropylene (PP)/polyamide 6 (PA6) blends on a lab-developed WAIM experimental platform. The experimental and theoretical methods were combined to investigate the effect of processing parameters on the residual wall thickness (RWT), surface quality and mechanical properties of the pipe obtained from WAIM. The results indicated that the RWT decreased gradually with increasing the melt temperature, mold temperature and water injection pressure, and however it increased with an increase in water injection delay time. Moreover, the tensile strength of the pipe increased gradually with the increase of mold temperature and water injection delay time. Nevertheless, when the melt temperature and water injection pressure were improved, the tensile strength tended to decrease gradually. The processing parameters affected the temperature field and therefore influencedthe nucleation and crystal growth as well as the final crystallinity. The higher the degree of crystallinity, the higher was the tensile strength of the pipes.