The invention discloses a speed change tool which comprises a motor, an output shaft, a gear transmission mechanism connected with the motor and the output shaft and a control system, wherein the control system comprises a control unit and a driving device, and the driving device is provided with a moving piece capable of moving between a first position and a second position in the gear transmission mechanism. When the moving piece is positioned at the first position and the second position, the output shaft has different output characteristics; and when a load torque is changed to a preset value, the control unit firstly adjusts the torque transmitted by the motor to the gear transmission mechanism and then controls the driving device to realize automatic gear shifting. The speed change tool can solve the problem of tooth beating generated in the process of the automatic gear shifting, thereby improving the electrical property of the tool and prolonging the service life of the tool.