Abstract: On the basis of the method of large deformation analysis, the paper carries out a vast amount of 3 D FEM numerical simulation and prediction on the deformation and failure possibility of the rockmasses surrounding the tunnels under various geostress, mechanical parameter and excavating conditions in Taiwan. The rockmasses concerned belong to grade Ⅴ and Ⅵ according to the Taiwan classification system of tunnel’s surrounding rockmass. A series of curves that predict the rockmass deformation have been drawn and the conclusion reached is of significance to guiding both designing and constructing of tunnels in future.