Abstract: The influences of Mg content on the microstructure and mechanical properties of Al-6.5Si-5.5Cu-xMg-0.2Zr-0.01Sr-0.06Ti-0.2Ce alloy were investigated by OM, XRD, TEM and tensile experiments, etc. The results show that Mg can coarsen and aggregate the eutectic Si phase, in addition to the coarsening of intermetallic compounds at grain boundaries. With the increase of Mg content, the number of θ（Al₂Cu） and Q phases（Al₅Cu₂Mg₈Si₆） in the matrix decrease, meanwhile the dislocation density decreases. The precipitates size and adjacent spacing inside the grains of the specimen containing 1.89 wt%Mg are larger than the specimen containing 0.88 wt%Mg, which weakens the second phase strengthening effect of the alloy. In addition, the wide precipitation-free precipitation zones（PFZs） of the specimen decrease its elongation. The mechanical properties deteriorate with Mg content increasing, so the specimen containing 0.88 wt%Mg has the highest tensile strength and elongation of 412.83 MPa and 6.23%, respectively.