Abstract: The extrusion casting experiments of Al-Si-Cu-Mg alloy at different casting temperatures were carried out. The effects of different casting temperatures on the microstructure, density and mechanical properties of the extrusion casting alloy were studied by means of microstructure observation, density test and tensile test. The results show that with the increase of casting temperature, the secondary dendrite arm spacing of Al-Si-Cu-Mg alloy decreases first and then increases, and the secondary dendrite arm spacing of the alloy cast at 710 ℃ is smallest, which is 16.9 μm. With the increase of casting temperature, the density, tensile strength and elongation of the extrusion casting alloy firstly increase and then decrease. The Al-Si-Cu-Mg alloy cast at 710 ℃ has the highest density and the best mechanical properties.