Process modeling of metal melt flow in porous media plays an important role in casting of metal matrix composites. In this work, a mathematical model of the metal melt flow in preform ceramic particles was used to simulate the flow behavior in a mold cavity. The effects of fluid viscosity and permeability (mainly affected by porosity of ceramic preforms) on the flow behavior were analyzed. The results indicate that ceramic porous media have a significant effect on the flow behavior by contributing to a low filling velocity and sharp pressure drop in the cavity. The pressure drop has a linear relationship with the fluid velocity, and a nonlinear relationship with porosity. When the porosity is relatively small, the pressure drop is extremely large. When porosity exceeds a certain value, the pressure drop is independent of porosity. The relationship between viscosity and porosity is described, and it is shown that the critical porosity changes when the viscosity of the melt changes. However, due to the limited viscosity change, the critical porosity changes by less than 0.043.