Abstract: The post-buckling behavior of composite laminates subjected to thermal loads and mechanical loads at the same time is studied using geometrically nonlinear 3-D finite element analysis. The major feather of this method is that every 3-D element contains several layers of different materials and plied orientations. The gap element is used to prevent the overlap of the delamination. The strain energy release rate is studied along the delamination front. The results show that the temperature affects the delamination damage significantly.