This work is based on a generalization of the mixed mode integral for three-dimensional crack problem. A new integral parameter in real three-dimensional case, which computes the energy release rate for each fracture mode, is developed. This integral provides the computation of stress intensity factors and energy release rate for each fracture mode. The virtual mechanical displacement fields is used in order to separate numerically mode I, mode II and mode III in the mixed mode ratio. A numerical validation, in terms of energy release rate, is carried out on a MMCG specimen under mixed-mode loading for different crack growth thickness. The non-dependent integration domain property is justified and the evolution of energy release rate along the thickness is evaluated.