The invention relates to a technology for constructing a super large span dome of an underground nuclear reactor plant cavern by preserving a center rock pillar. The technology comprises the following steps: (1) preserving the center rock pillar in the center part of the dome; (2) breaking through a construction passage to the center rock pillar along the semi-diameter of a spherical plane where the dome is located, supporting an excavation exposed surface of the construction passage, and reinforcing a middle support of the excavation exposed surface; (3) symmetrically excavating in a fan shape along the left side and the right side of the construction passage, reinforcing middle temporary supports of working faces, supporting an exposed dome outline rock surface, and reinforcing supporting for dome outline abuts; (4) after the completion of excavation, removing the center rock pillar from top to bottom. The technology is applied to constructing all large span domes, in particular to the super large span domes of the underground nuclear reactor plant caverns, and has the technical advantages of simple excavation procedures, convenience in construction, safety and reliability.