During the past decades, the industry has been looking for several media as the assistant for injection molding. Among them, water assisted injection molding (WAIM) has been proven to be a pretty good way to fabricate hollow or more complicated parts. Water is chosen because of its low cost. Further, water has significant thermal conductivity that can provide more effective cooling to reduce the cycle time of the process. In addition, it is similar to gas assisted that water also can provide packing/holding effect to reduce the shrinkage and warpage to yield good quality products. Hence, several suppliers have been involved in developing this class of techniques and equipments. However, to obtain better products, a number of questions regarding to the material properties and process conditions, need to be fully understood. In this study, the complex flow behavior of melts under the assistance of injected water is conducted by examining the coupling effects of the process conditions and the material properties numerically. Further, the verification is performed experimentally as well.