Due to the flow behavior of metal melt affected by the back pressure from residual gas in the mould during high pressure die casting （HPDC） process

the back pressure conditions should be considered in order to simulate the filling process precisely. Filling process of an aluminum alloy filter for automobile in HPDC was simulated by introducing back pressure conditions

and the simulated results were well in agreement with actual ones. The modified design was conducted based on the simulated results. The defects in the castings can be effectively eliminated by adjusting the position of the vents to change the back pressure in local cavity and then to affect the filling distribution of liquid aluminum alloy.