The invention relates to an electrician instrument, in particular to a fastener for a valve core of a butterfly valve. The fastener is characterized in that a circular tube (1) is arranged on the fastener for the valve core (6) of the butterfly valve (5); two opposite bosses (2) are arranged at one end of the circular tube (1); an inserting hole (3) is formed in the tube wall of the other end of the circular tube (1); the inserting hole (3) is matched with a wrenching rod (4). The fastener for the valve core of the butterfly valve has the beneficial effects that the two bosses of the circular tube are inserted into a groove in the annular end surface of the upper end of the valve core, the valve core can be fastened through the wrenching rod, and leakage caused by loosening of the valve core is prevented; in addition, the fastener has the characteristics of being simple in structure, convenient to operate and the like; the fastener is expected to become necessary equipment for maintaining an oil filling butterfly valve of a transformer or an oil-inrush-type reactor.