Since the pioneering work of Paris and Erdogan (1963), the fatigue crack growth (FCG) model has been being modified by worldwide researchers. Research efforts have been devoted by a number of investigators for assessing the fatigue condition of structural components by means of residual stress at the crack tip, threshold stress intensity factor, load ratio, and so on. The parameter C is always as a constant about material and structure, and almost no further research on it. In this paper, we proposed a novel analytical approach to predict the effect of the parameter C on fatigue performance. The inertial effect coefficient model for FCG under constant amplitude (CA) loading is briefly described and then used to verify the parameter C is a variable and analyze the relation between the parameter C and FCG rate. The prediction of the parameter C in this model is in good agreement with experimental data taken from the literature.