Using a two-dimensional discrete dislocation dynamics and finite element coupling method, numerical simulations were performed on the dislocation evolution and fracture behavior of FCC structured nickel-based single crystal under loading-relaxation-reloading conditions. The model comprehensively considers mechanisms of dislocation nucleation, slip, and annihilation, achieving autonomous crack evolution through the dynamic coupling of dislocations and damage fields without the need to preset the expansion path. The simulation results show that the relaxation process can effectively reduce stress concentration around the crack tip, delay crack initiation, promote crack path deflection and multiple slip system activation. Quantitative analysis indicates that the strain energy release characteristics during the relaxation process is positively correlated with the initial dislocation density, with high-density dislocation systems exhibiting a faster energy equilibrium process.