The utility model discloses an installation structure for a containment dome of an underground nuclear power station reactor cavity. The installation structure comprises a containment barrel; an annular crane rail bearer is arranged on the inner wall of the upper part of the containment barrel; a crane girder is arranged on the annular crane rail bearer; the two sides of the crane girder are respectively provided with multiple support mudsills, wherein one end of each support mudsill is connected with the annular crane rail bearer; multiple stand columns of concentric circles structures are arranged on the top faces of the annular crane rail bearer, the crane girder and the support mudsills; a ring beam for supporting the containment dome is arranged on each circle of stand columns; stand column sidestays are arranged between the adjacent stand columns. According to the installation structure for the containment dome of the underground nuclear power station reactor cavity, the technical problem that integral hoisting of the containment dome cannot be performed in the underground nuclear power station reactor cavity due to the limited underground space can be solved, and the installation structure can be widely used in the technical field of nuclear power.