The refining effect of rare earth flux on aluminum melt was studied based on the principle of adsorption purification, and the effect of composite flux on aluminum melt purification and mechanical properties of alloy was studied by means of optical microscope, scanning electron microscope and mechanical properties test. The results show that the composite flux with the proportion of 689% chloride, 86% calcium carbonate and 51% lanthanum fluoride has the best effect on the purification of aluminum melt, the porosity of the alloy sample decreases from 825% to 132%, the hardness increases from HB917 to HB993, the elongation increases from 053% to 112%, and the tensile strength increases from 1139 MPa to 2290 MPa.