Buoy for mounting underwater overweight component

A buoy for mounting an underwater overweight component comprises an external shell and an internal framework. The external shell is connected with a vent pipe, and the vent pipe is communicated with an internal cavity of the buoy. A reserved cavity is formed in the internal cavity of the buoy, a relief hole is formed in the bottom of the reserved cavity, and a water injection hole valve and a valve opening part are arranged at the bottom of the external shell of the buoy. According to the buoy for mounting the underwater overweight component, the weight of a lifting component of a lifting appliance within a working range is effectively increased, and the working range of the lifting appliance is remarkably increased even if the component with the same weight is lifted.