Extensive study has been conducted on the repair technique using carbon fibre reinforced polymer (CFRP) materials to improve the load carrying capacity or to extend the fatigue life of structural steel elements. However, less is reported about the effectiveness of this method when applied at different stages of crack propagation. This paper presents a numerical study on cracked steel plates (with different degrees of damage) repaired by CFRP laminates using the boundary element analysis system software (BEASY). Values of stress intensity factor and fatigue lives were evaluated with corresponding boundary element models. Different degrees of damage were simulated using different lengths of initial cracks, representing the multiple stages of crack propagation. The numerical results were compared well with the experimental data. The results showed that, regarding to the residual fatigue life, the improvement of the fatigue life was more pronounced under higher damage degree. Covering the initial cracks with CFRP and using ultra-high modulus CFRP laminate and could lead to more significant strengthening effects.