Abstract: The conception of multiphase flow and the two-phase flow models were introduced into the field of powder injection molding (PIM). The single-fluid model, two-fluid model and Eulerian-Lagrangain model for describing the powder-binder filling flow process were discussed. The characteristics of each model were briefly analyzed. Simulation results showed that the two-fluid model was fitter than the single-fluid model for describing the powder segregation, powder concentration and other special phenomena arising in PIM. Furthermore, the two-fluid model is easier to reach convergent than the Eulerian-Lagrangain model in simulating the PIM process.