Abstract: Basing on the equations of continuity, momentum balance, energy balance and engergy balance at the solid-melt interface, a mathematical model of mold filling process with solidified layer forming on the inside mold surface was estabilished by finite difference method. Variations of the thickness of the solidified layer as a function of time, volumetric flow rate and mold temperature was presented. The simulation results show that the initial thickness of solidified layer near the gate increases quickly, while it's accumulated rate decreases slowly. the greater volumeric flow rate, the thinner thickness of solidified layer. It is favorable to filling process if the mould temperature rises properly,which decreases the solidified layer thickness.