This paper presents an improved numerical simulation procedure for fatigue crack growth based on the strip yield model with a weight function. In the previous numerical model, one-dimensional bar elements plugged up the chink corresponding to the virtual crack opening displacement in the plastic zone to describe the crack wake over fatigue crack surfaces. However, this numerical simulation method gives poor growth estimations under large variable loading histories, e.g. spike overloading. It is possible that insufficient consideration of the strain hardening effect of materials leads to excess crack closure. The authors develop the numerical simulation model of fatigue crack growth by considering the strain hardening effect of materials using the modified strip yield model. Numerical simulations of fatigue crack growth under many types of loading are performed to investigate the validity of our new proposed model. Comparison of proposed simulation results with previous results and with experimental measurements confirms the superiority of the proposed method.