The effects of Er addition on the microstructure and mechanical properties of ZL201A aluminum alloy were studied via metallographic microscope, scanning electron microscope, transmission electron microscope, energy dispersive spectrometer, and mechanical property tests. Results show that the Er addition can refine the α-Al matrix from columnar grains into fine equiaxed grains. Additionally, the θ phase (Al₂Cu) is transformed from fine network structure into the dispersed fine particle structure. When the Er content reaches 0.4wt%, the grain refinement effect reaches the maximum state and the mechanical properties of the alloy are optimal. The average grain size of α-Al matrix is 19 μm; the tensile strength and the elongation are 298.14 MPa and 6.56%, respectively. The fracture mode also changes from brittle fracture to ductile-brittle fracture, which is beneficial to the practical application of aluminum alloys. When Er content exceeds 0.4wt%, the grain size increases and the mechanical properties of alloy decrease.