Abstract: The conception of equivalent powder was brought forward and the quasi-fluid hypothesis of powder was introduced for studing the powder segregation during powder injection molding(PIM).The governing equation of the two-fluid model was built by the hydrodynamic method,which described the process of PIM.The expression of interaction phase and the viscosity relationship between the powder and binder were studied.The simulation result based on the two-fluid model is in agreement with the result based on the single-fluid model by CFX software,verifying the credibility of the two-fluid model.