Abstract: In order to more accurately determine the strain field range of crack tip and quantitatively analyze the crack tip stress, the distribution of crack tip strain field during crack propagation of 2A12-T4 aluminum alloy FSW joint was obtained by digital image correlation method, and the stress intensity factor and plastic zone size evolution of 2A12-T4 aluminum alloy welded sample were calculated by finite element method.The size of the plastic zone at the crack tip was calculated by fracture mechanics method, and the finite element simulation results were compared with the calcuated results.The results show that the calculated results by finite element method are close to those by theoretical calculation method, and the error is within the allowable range.It shows that the finite element method is reliable for analysis of the stress intensity factor and the size of plastic zone at the crack tip.