Abstract: Effects of friction stir welding (FSW) process parameters on microstructure and mechanical properties of the LY12 aluminum alloy joint were investigated with orthogonal experiments.The results show that the shoulder diameter of the stirrer has greater effect on the tensile strength of the joint than rotation speed and weld speed.When the welding parameters are proper,the heat input could be optimized,the microstructure of weld nugget consist of almost fine equiaxed grains,tensile strength of the joint is higher than 350 MPa and the joint strength coefficient is 86%.