With its excellent mechanical properties, carbon fiber reinforced polymer (CFRP) can be applied to the repair and reinforcement of engineering structures. To research the repair performance of CFRP on cracked steel plate, the finite element model is figured out in this paper. Combined with fracture mechanics, the dependability of the model is verified. Considering the influence of prestress on the repair performance, the simulation analysis is implemented with fatigue life as evaluation indexes. The results show that CFRP can improve the fatigue life of steel plate, and the effect of prestressed CFRP is more obvious.