Abstract: The underground nuclear power plant takes the medium scale mountain terrain in hilly ground as its base, and the general layout of the nuclear island building is of "Terrace horizontal buried" style. Based on the layout scheme that locating the underground building of the nuclear island in L cavern and the ground building on the outside of the massif slop, the concept design of the general layout of the ground building of nuclear island as well as the equipment transport and personnel access, pipe and electrical cable connecting access of the underground building is conducted. The consequence by putting the traditional ground nuclear buildings under the ground is analyzed, and the analysis show that the layout scheme of the nuclear island building of the underground nuclear power plant is reasonable and feasible.