Abstract: The effect of heat treatment on the mechanical properties of A356 alloy modified with La-Ce rare earth was studied, the A356 alloy modified by La-Ce mixed rare earth was subjected to primary and secondary heat treatment at different temperatures and holding time. By SEM, tensile test, hardness test and other testing method, the mechanical properties of A356 alloy modified by La-Ce rare earth were characterized by different heat treatment processes, the optimum heat treatment process was obtained. The results show that the mechanical properties of A356 alloy after adding La-Ce mixed rare earth have been significantly improved after 540 ℃ ×5 h solid solution treatment +160 ℃ ×6 h aging treatment +180 ℃ × 8 h secondary aging treatment. The hardness, tensile strength and yield strength of A356 alloy with 0.45 wt% La-Ce mixed rare earth are 123.7 HV, 328 MPa and 280 MPa, respectively.