An efficient and simplified calculating method for estimation of crack opening displacement was proposed, and the method was applied to the analysis of fatigue crack closure mechanism and effective stress range ratio during crack growth process under cyclic loading. Crack opening displacement, crack closure stress and effective stress range ratio were calculated by the method and these values were compared with those obtained by Dugdale model analysis, finite-element method and various experiments, and good agreement was found among them, further more various factors affecting on the effective stress range ratio were discussed. From the above results, the proposed method is considered to be a very useful tool for the calculation of crack opening displacement, analysis of fatigue crack closure and propagation phenomenon.