Water assisted injection molding technology has become one of the most important methods to manufacture hollow plastic parts in recent years, dice to its light weight, relatively lower resin cost per part and faster cycle time. This report aims to present a review of the development and progress of the wetter assisted injection molding technology. The tooling used for the process is introduced. The interaction between the assisting water and the polymer melt during molding is discussed, and insight into the penetration behaviors of the fluid is summarized. In addition, comparisons have been made between the gas-assisted injection molding and water assisted injection molding processes.