Polymeric Due to high strength to weight ratio of polymeric composites and their directional properties, they are extensively used in engineering, particularly in aerospace industry. However, the difference in material properties of composites makes their failure prediction complicated especially under cyclic loading. Present study is carried out to develop a new method for estimation of the intralaminar fatigue damage of fibrous composites based on continuum damage mechanics. In order to include the influence of microscopic defects in three material orientations, three internal material state variables namely damage variables are defined in thermodynamics framework. By considering a 3-directional damage propagation, suggested model is able to make a good prediction of laminated composites fatigue life. To achieve this, a closed form solution by energy method in framework of thermodynamics is presented. The solution is in a way to include the differences in damages of various directions yet maintaining the independency on the layup. The model is implemented in ANSYS software by using a user material code (Usermat). This method gives us an advantage to estimate the fatigue life of any laminate with arbitrary layup under different loading conditions only by having static and fatigue properties of a unidirectional ply. Characterization of constants of model is presented and they are also determined for a certain composite material. Comparison between the predicted results of proposed model and the available experimental data verifies the great precision of the model.