The oxide inclusion formation tendency in tilting cast magnesium alloys intake manifold was studied by numerical simulation. Two different programs were used for results comparison. The results indicate that it was easier to form oxide inclusion when connecting foundry ladle with the junction panel of intake manifold instead of cavity resonator. The oxidation mixture is prone to appear at the ribs and outer wall of the four main air piles of the intake manifold. The formation of oxide inclusion would be influenced by the flowing state of the melt during casting process.