Abstract ln two previous papers, CFRP reinforcements of fatigue damaged steel components were examined. For this purpose; CFRP lamellas glued on, either limp or pre-tensioned, were tested. The result of the reinforcement is an increased remaining service life. In order to understand the tests, numerical simulations with Abaqus based on XFEM were carried out in this paper. The simulations show (like the previous tests), in comparison with the unreinforced reference samples, a significant reduction in the stress on the crack tips through the application of CFRP lamellas. This shows the significantly longer remaining service life. ln addition, the parameter studies show that the remaining fatigue life is obviously influenced by the prestress, the stress range of cyclic loading, the initial crack length and the CFRP width.