The P+Sr+Ce compound modification technologies of as-cast Al-21Si-1.5Cu-1.5Ni- 2.5Fe-0.5Mg alloy were investigated by means of orthogonal test. Orthogonal test results show that 3% (CaH_2PO_4+2CaSO_4)+0.2%Sr+0.2%Ce is the optimum additive of modification treatment which can fine eutectic and primary silicon also can change the form of rich-iron phase at same time. The needle form of rich-iron phase is (Al_9FeSi_3), which is prored by X-ray diffraction analysis and X-ray energy spectrum analysis. After compound modification treatment, the needle form of rich-iron phase disappeared and the fish bone form of rich-iron and rich-Ce phase that is Al_8CeFe emerged. Both at room temperature and at 300 ℃, the tensile strength of the alloy after the modification treatment with the optimum additive is 30% lager than that of the alloy unmodified. Observed by SEM, the brittle intercrystalline tensile fracture changed into a blended one in which has many dimples. The P + Sr + Ce compound modification technologies of as-cast Al-21Si-1.5Cu-1.5Ni- 2.5Fe-0.5Mg alloy were investigated by means of orthogonal test. Orthogonal test results show that 3% (CaH_2PO_4 + 2CaSO_4) + 0.2% Sr + 0.2% Ce is the optimum additive of modification treatment which can fine eutectic and primary silicon also can change the form of rich-iron phase at same time. Which needle form of rich-iron phase is (Al_9FeSi_3), which is prored by X-ray diffraction analysis and X-ray energy spectrum analysis. After compound modification treatment, the needle form of rich-iron phase disappeared and the fish bone form of rich-iron and rich-Ce phase that is Al_8CeFe emerged. Both at room temperature and at 300 ° C, the tensile strength of the alloy after the modification treatment with the optimum additive is 30% lager than that of the alloy unmodified. Observed by SEM, the brittle intercrystalline tensile fracture changed into a blended one in has has many dimples.