The invention aims to disclose an openable inflatable nuclear island containment temporary top cover. The top cover comprises a supporting device arranged at the top of a nuclear island containment inadvance, and an annular motor rail is laid in the inner side of the supporting device; a plurality of motors are arranged on the motor rail, and an automatic rope coiling device is arranged on the motors; the automatic rope coiling device makes an inflatable membrane structure with a flexible inflation channel connected with the motors through ropes; the other end of the flexible inflation channel is connected with an air blower. Compared with the prior art, the top cover is directly installed on the reactor containment, can be opened or closed in a large area, meets hoisting operation requirements of a reactor plant, is simple in structure, high in applicability and convenient to install, can be opened and closed many times in a day, is high in opening and closing efficiency and light instructure, has little stress influence on the containment, can quickly respond to environment and weather changes, improves the construction efficiency, is very practical and achieves purposes.