The effect of the rare earth Y addition on the microstructure and mechanical properties of ZL205A alloy was studied by OM, SEM and XRD before and after heat treatment. The fluidity of the alloy was also tested. Results show that when the content of Y is 0.2wt% and 0.3wt%, the grains refinement effect is better. With the increase of Y, the θ phase distribution transforms from reticular into dendritic, and the yield strength and tensile strength decrease. Trace Y addition decreases the fluidity of ZL205A alloy. When the Y content is 0.3wt%, the tensile strength and the ductility increase significantly after T6 heat treatment. Heat treatment process can reduce the composition segregation of alloys and improve the microstructure, resulting in a better comprehensive mechanical performance. After adding a small amount of Y, the compound AlCuY, which has high melting point, low strength and is difficult to be melted, can decrease the amount of θ phase, which is an important reason to the declined mechanical properties.