Abstract: Experiments of water assisted injection molding (WAIM) were carried out on a labdeveloped system to investigate the influences of parameters such as water pressure, water temperature, and water injection delay time on overflow WAIM process. It showed that the higher the water-injection pressure, the thinner the residual wall thickness and the more smooth and bright the inner surface. Water eccentric penetration occurs under low waterinjection pressure. Increasing water-injection pressure led to a less eccentric water penetration. Water temperature had less influence on the residual wall thickness. Increasing waterinjection delay time increased the residual wall thickness and reduces the water eccentric penetration under low water-injection pressure effectively.