A method for hoisting and transporting assemblies in an underground nuclear power plant, the method including: 1) pouring concrete onto a reactor cavern to form a rock anchor beam; hoisting a circular bridge crane to the reactor cavern through a hoist shaft on a top of the reactor cavern; mounting the circular bridge crane on the rock anchor beam by using a truck crane; 2) installing a containment cylinder and a track beam of a polar crane in the reactor cavern using the circular bridge crane; hoisting a gantry crane on one end of a polar crane girder and sending the polar crane girder to the reactor cavern; hoisting the other end of the polar crane girder using the circular bridge crane; allowing the polar crane girder to be horizontal; and mounting the polar crane girder on the track beam.