According to the fatigue crack propagation behavior of complex shape welds in actual engineering application and based on the Paris rate propagation model,the M-integral independent of the integral path is used to calculate the stress intensity factor of the crack front. And the stress intensity factor at the intermediate point of the crack front is used as the control parameter of crack propagation. Adopt different crack propagation direction criterion,and the initial surface crack of the weld toe is described by a semicircle. Simulate the dynamic evolution process of the entire crack front at different propagation stages. The fatigue crack growth is divided into three stages. The distribution and variation of stress intensity factors K,Ⅰ,K,Ⅱ, and K,Ⅲ, of crack front in different propagation stages are calculated and compared. The influence of crack load type on fatigue crack growth is revealed,and the proportion of fatigue life in different expansion stages is calculated.