The invention discloses an underground nuclear power plant reactor chamber containment dome installing structure, which comprises a containment tube body, wherein an annular crane rail beam is arranged on the inner wall of the upper part of the containment tube body; a crane girder is arranged on the annular crane rail beam; a plurality of support bottom beams with one ends connected with the annular crane rail beam are respectively arranged at the two sides of the crane girder; a plurality of upright posts of concentric circle structures are arranged on the top surfaces of the annular crane rail beam, the crane girder and the support bottom beams; the tops of each circle of upright posts are provided with annular beams used for supporting a containment dome; and upright post inclined supporters are arranged between the adjacent upright posts. The underground nuclear power plant reactor chamber containment dome installing structure solves the technical problem that the containment dome integral suspended installation cannot be carried out in an underground nuclear power plant reactor chamber due to the limitation of an underground space, and the underground nuclear power plant reactor chamber containment dome installing structure can be widely applied to the technical field of nuclear power.