The invention relates to a torsion specifying device of a pneumatic wrench used for the electric power industry. The torsion specifying device comprises a cylinder body of which one end is sealed and one end is open and the shape is cylindrical, a center shaft, a supporting body which is installed at the open end of the cylinder body via a set screw, internal spring sheets which are installed at the position, which is close to the sealed end, in the cylinder body, and external spring sheets which are installed at the position, which is close to the supporting body, in the cylinder body. When a bolt is screwed, the size and the number of the spring sheets in a torsion ring are adjusted according to the specified torque so as to be set to the required torque, and thus adjustment is convenient and easy. When torque of the screwed screw and nut reaches the required torque, the cylinder body is affected by equal restoring torque, and the spring sheets enter the phase of elastic deformation. The spring sheets slip out of the ratchet slot in the cylinder body due to elastic deformation, and the spring sheets rotate relative to the cylinder body so that the cylinder body stops selecting and the screwed screw and nut are enabled not to be stressed.