Abstract: In terms of the different aspect ratio of initial crack in weld toe, the numerical simulation of crack propagation was carried out based on the NASGRO crack growth rate model. Semi-ellipsoid with different aspect ratio was used to characterize the surface crack of weld toe. Considering the short crack propagation stage, M integration was used to calculate the stress intensity factor of the whole crack front and the median value of crack front stress intensity factor was taken as the main control parameter for crack propagation. The shape evolution stress intensity factor distribution and change of crack front were simulated and analyzed under different aspect ratio. The results show that with propagation of the crack, the different shape of the short crack tend to be more consistent; The shapes of the short cracks have a greater influence on the early crack propagation and eventually lead to significant differences in the overall fatigue life; Based on the influence of the initial aspect ratio on the stress intensity factor, the extended shape, the fatigue life of the crack front, and the inflection point of its effect can be used as an effective reference to define the short crack and the long crack. The fatigue test of cross welded joint was carried out. The test results show good agreement with and simulation results.