The powder-binder separation is a common difficulty during injection molding, which leads to the inhomogeneity in the debinding and sintering stages. Previous studies focus on the relationship between "final results" and "initial conditions", while the dynamic filling process of feedstock and the evolution of powder-binder separation were ignored. This work investigated the effects of filling patterns on the powder-binder separation during powder injection molding. The mold filling model of PIM has been developed, based on the multiphase fluid theory and the viscosity model of feedstock. Parameters of the viscosity model were modified by the experimental data. Numerical simulations were compared with experiments with the same process parameters. The powder-binder separation phenomena in green bodies were detected by X-Ray computed tomography (CT). The experimental phenomena were explained clearly by the evolution of powder-binder separation obtained with numerical simulation method. A typical compacting filling pattern of PIM and filling mobility variable of the feedstock were proposed. A proper filling pattern was helpful to ensure the mobility of feedstock and the homogeneity of green body. (C) 2014 The Authors. Published by Elsevier B.V.