Fatigue crack propagation behavior under simulated whipping loadings which contain two different frequency components is highlighted. Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history. The critical value of the plastic hysteresis for the stress versus strain relationship occurring in the vicinity of a crack tip is defined as the control parameter for extracting the effective loading history. Comparison of fatigue crack propagation curves obtained from the improved numerical simulations with the measurements which were conducted by Sumi (2010) is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superposed loading history containing different frequencies. In addition, imperfection of the S-N curves approach, which corresponds to the combination of the linear cumulative damage law and the loading cycle count by the rain flow method, is conducted.