The invention puts forward a flexible connection head used for the bolt fastening operation of transformer substation electrically charged equipment, a bolt fastening tool of the transformer substation electrically charged equipment, and a robot system. The flexible connection head comprises an upper universal joint, a lower universal joint and a connecting rod, wherein the upper universal joint and the lower universal joint are connected through the connecting rod; the lower universal joint consists of a half convex universal joint and a half concave universal joint, wherein the half convex universal joint and the half concave universal joint are cooperatively connected; grooves are formed in the half convex universal joint and the half concave universal joint respectively; a magnetic regulation rod and an aligning spring are installed in the grooves in a clearance fit way; and the aligning spring is used for regulating the movement direction of the magnetic regulation rod to form a buckle in the position connected with a sleeve so as to realize fixed connection between the flexible connection head and the sleeve. The bolt fastening tool can realize a bolt assembling and disassembling operation in four quadrants, and the degree of freedom of the bolt fastening tool is increased. While the aligning spring, the connecting rod, the upper universal joint and the lower universal joint of the flexible connection head realize torque transmission, the rigidity of the flexible connection head is guaranteed.