The CAE technology is very important in the design of the gas-assisted injection mold. The models of the viscous and mathematics when the melt fluids in the mold cavity during filling and pressure was hold during the pack process were described. The way that the mathematics model was reasonable predigested was introduced. The gas-assisted molding for the automobile bumper mold was simulated by C-MOLD which is one of the CAE software. The effect and process of the gas filling were optimized. The appeal quality and the dynamic capacity were improved and the proportion of the first-try was increased.