The invention discloses a mountain land fully-buried underground nuclear power station. The mountain land fully-buried underground nuclear power station comprises a nuclear island and a conventional island. Nuclear buildings of the nuclear island are arranged in a mountain nuclear island cavern group. The conventional island is arranged in a mountain conventional island cavern group. The mountain land fully-buried underground nuclear power station is suitable for terrain environments where no large ground platforms are arranged on precipitous mountains, outer sides of side slopes and the upper portions. Feasible general arrangement is provided for construction of underground nuclear power stations. Engineering has economic feasibility. Compared with a ground nuclear power station, no large adjustment is needed by the main process system, and the technology research and development difficulty of underground nuclear power stations is lowered. By arranging nuclear island plants and conventional island plants in different underground caverns, it can be ensured that the existing underground engineering technology meets the requirement for arranging the nuclear buildings of the nuclear power stations underground.