A construction layout for caverns of an underground nuclear power plant, including: two primary caverns accommodating nuclear reactor powerhouses, combined caverns, electric powerhouse caverns, pressure relief caverns, a first primary traffic tunnel, a second primary traffic tunnel, a third primary traffic tunnel, a top adit system, and a ground adit system. Each combined cavern is disposed on one side of each of the two primary caverns. Each electric powerhouse cavern and each pressure relief cavern are disposed on two sides of each of the two primary caverns perpendicular to the longitudinal direction of the mountain. Each electric powerhouse cavern is perpendicular to the longitudinal direction of the mountain. The first primary traffic tunnel and the third primary traffic tunnel are disposed along the longitudinal direction of the mountain on outer sides of the two combined caverns, respectively.