In this paper, the effect of Cu content on the tensile properties of Al-Si-Mg-Er-Zr alloy at room temperature and high temperature was studied. They were α-Al, Si, β, Q and θ phases in the as-cast Al-Si-Mg-Er-Zr alloys with different Cu contents. With the increase of Cu content, the eutectic microstructure of the alloy increases, and it is bone-shaped, which is conducive to improving the casting performance of the alloy. With the increase of Cu content, the yield strength of as-cast alloys increases. Three Al-Si-Mg-Er-Zr alloys with different Cu content (0.6Cu, 1.0Cu and 1.0Cu) were heat treated under 500°C/4h+540°C/2h+180°C/xh, and they reached peak aging at 10h, 12h and 12h, respectively, and the peak hardness was 137.2HV, 139.2HV and 142.7HV, respectively. With the increase of Cu content, the room temperature tensile strength of the alloys under T6 temper increases, which is due to the fact that the alloy containing 1.4Cu has the most strengthening phase, including β ? ? phase, Q ? phase and θ ? phase. After 44 hours of soaking at 300°C, the hardness of the alloy containing 1.4Cu decreased the least, this is because, at 300 ℃，with the increase of the Cu level, the amount of the Q-Al5Mg8Cu2Si6 precipitates increases, and the Q-Al5Mg8Cu2Si6 phase is the main thermo-dynamically stable precipitate at 300 ℃ and improved the heat resistance of the alloy. The elongation at 300°C of the three Cu alloys under T6 temper was higher than that of room temperature tensile, and the fracture form also changed from brittle fracture at room temperature to ductile fracture at 300℃.