The invention relates to a fixed torque screwdriver which is designed to overcome the defects that the prior known fixed torque screwdriver has a complex structure, high cost, large volume and operation inconvenience. The fixed torque screwdriver comprises an operation handle and a core rod; the operation handle is provided with a hollow cavity; the core rod is provided with a screwdriver head; the core rod is provided with a gear A, a gear B and an elastic element on one end of the cavity of the operating handle; the gear A rotates along with the operating handle and is in transmission connection with core rod; the gear B and the gear A are mutually occluded; the elastic element is supported against the gear B to exert pressure to overcome the axial separation force generated between the gear A and the gear B when the gear A drives the core rod to rotate; and the fixed torque of the fixed torque screwdriver depends on the parameter values of the elasticity of the elastic element. The fixed torque screwdriver disclosed by the invention has a simple structure and small volume, is convenient to operate and can achieve the purpose of limiting the torque. In addition, the fixed torque screwdriver is especially suitable for mounting and demounting the standard screw, can be operated conveniently by consuming the shortest time and can ensure that the service life of the standard screw can be prolonged.