This article presents the development of a fatigue damage model which helps to carry out simulation of the evolution of delamination in the laminated composite structures under cyclic loadings. A classical interface damage evolution law, which is commonly used to predict the static debonding process, is modified further to incorporate fatigue delamination effects due to high cycle loadings. An improved formulation is also presented to incorporate the ‘R’ ratio effects. The proposed fatigue damage model is identified using fracture mechanics tests like double cantilever beam, end-notched-flexure and mixed-mode bending. Then a non-monotonic behavior is used to predict the fatigue damage parameters able to carry out delamination simulations for different mode mixtures. Linear Paris plot behaviors of the above-mentioned fracture mechanics tests are successfully compared with available experimental data on HTA/6376C and AS4/PEEK unidirectional materials.