Abstract: 2 mm thick 2A12 aluminum alloy was welded by refill friction stir spot welding, and the welding temperature field and thermal cycle were numerically simulated based on three-dimensional heat flux coupled finite element method. The results show that with the increase of rotation speed, the welding peak temperature and high temperature residence time increase.When the rotation speed is higher than 2000 r/min, the component liquefaction occurs in the stirred zone of the joint, and the eutectic structure enriched by Cu and Mg elements is formed, which shows U-shaped line characteristics in the cross section of the joint. When the welding speed is 2000, 2500 r/min, the crack initiates and propagates preferentially in the component liquefaction zone under tensile load, and the tension-shear load of the welded joint is 7.6, 7.8 kN, respectively.When the welding speed is 1500 r/min, the component liquefaction is restrained and the tension-shear load of the joint is increased to 8.0 kN.