Abstract: The weld toe radius has a significant impact on the fatigue performance of welded structures. By integrating the Voronoi tessellation method and submodeling technique, a two-dimensional microscopic representative volume element (RVE) submodel was constructed at the macroscopic cruciform welded joint weld toe using a viscoplastic rate-related crystal plasticity constitutive model. The average fatigue indicator parameters of the slip band were calculated to determine the nucleation life and extension life of the slip band. The formation of cracks was simulated by reducing the elastic modulus of the slip band with the shortest life, realizing the simulation of macro-micro scale fatigue short crack evolution behavior. Analysis shows: when the weld toe radius is less than 0.5 mm, the nucleation life increases with the increase of the weld toe radius; when the weld toe radius is greater than 0.5 mm, the nucleation life mainly fluctuates due to the influence of grain shape and orientation. The weld toe RVE submodel can be divided into the weld toe arc influence zone and the non-influence zone. In the influence zone, the crack evolution behavior is mainly affected by the weld toe radius, with different nucleation positions and the extension rate increases linearly with the number of crack cycles; as the crack extends, the influence of the weld toe radius gradually decreases, and the influence of grain shape and orientation gradually increases; when the crack extends to the non-influence zone, the crack evolution behavior is mainly affected by the grain shape and orientation, and the extension rate shows significant fluctuations.