The mechanisms for the selfsupport ability of the surrounding rock mass are discussed. Conclusion is drawn that the selfsupport ability of the surrounding rock mass originates from the strength of the surrounding rock mass and that the plasticallystrengthened zones and the elastic zones of the surrounding rock mass are the major loadbearing structures. NATM’s viewpoint that the selfsupport ability of the surrounding rock mass should be fully exerted can be further described as that the initial state of the surrounding rock mass should be basically maintained, which is an explicit expresstion. This conclusion provides a technological direction and has certain operationability. The minimumenergy principle is applied in rock tunnels, soil tunnels and tunnels located in fractured ground respectively. The meaning of the minimumenergy principle is expounded thoroughly. It is stated that the minimumenergy principle can be used as one of the criteria to determine whether each construction plan is good or not.