The effects of vacuum degree, pattern density, pouring temperature and metallic static head on the mold-filling velocity of AZ91D alloy in the expendable pattern casting (EPC) process have been investigated in the paper, and the influencing law of these technological factors on the mold-filling velocity are obtained. The results indicate that the influence of vacuum degree on the mold-filling velocity of AZ91D alloy in the EPC process is greatest, pattern density and pouring temperature are next respectively, and metallic static head is small relatively.