Abstract: Aimed to the quality of waterassisted injection molded parts, this paper presented a survey for their defects and relevant process optimization from the macroscopic phenomena such as the first penetration process of highpressure water instability, the phenomenon of melt accumulation at the mold cavity variable cross section, the formation of water fingerings during the process and the microscopic phenomena like fiber orientation and distribution along the thickness of the parts, and crystal types and structures in different regions.