Abstract: Aiming at the existence of multiple cracks at the weld toe, the numerical simulation of the multi-crack propagation process was carried out. Consider the short crack growth stage. The M-integral is used to calculate the stress intensity factor of the entire crack front. The specific influence of this factor on the propagation behavior before and after the fusion of the crack front is simulated and analyzed. The results show that the difference in crack spacing will directly lead to the difference. The influence of the stress intensity factor before and after the fusion of the crack front is different. The shape of the crack front has different shapes due to the initial crack spacing. The relative crack spacing L/a=1 boundary inflection point can be used as an effective reference for subsequent engineering research. The fatigue test of the cross-welded joint was carried out, and the simulation results were verified.