A power tool , comprising: a housing ; an electric motor disposed in the housing ; a driver circuit electrically connected to the electric motor to drive the electric motor to operate; a speed detection device configured to acquire a rotational speed of the electric motor ; and a control device connected to the speed detection device and the driver circuit , wherein the control device is configured to output a control signal to the driver circuit to control rotation of the electric motor ; wherein the control device is configured to acquire the rotational speed of the electric motor , and to obtain within a preset time a rotational speed variation of the electric motor based on the rotational speed of the electric motor ; characterized in that the control device is further configured to control the electric motor to be in a start-up stage when the rotational speed of the electric motor is less than or equal to a preset target rotational speed; and for over-torque protection of the electric motor to turn off in the start-up stage the electric motor when the rotational speed variation is less than a rotational speed variation threshold; and to control the electric motor to be in an operation stage when the rotational speed of the electric motor is greater than the preset target rotational speed; and to control in the operation stage the electric motor in a control manner providing a stable output torque. a housing ; an electric motor disposed in the housing ; a driver circuit electrically connected to the electric motor to drive the electric motor to operate; a speed detection device configured to acquire a rotational speed of the electric motor ; and a control device connected to the speed detection device and the driver circuit , wherein the control device is configured to output a control signal to the driver circuit to control rotation of the electric motor ; wherein the control device is configured to acquire the rotational speed of the electric motor , and to obtain within a preset time a rotational speed variation of the electric motor based on the rotational speed of the electric motor ; characterized in that the control device is further configured to control the electric motor to be in a start-up stage when the rotational speed of the electric motor is less than or equal to a preset target rotational speed; and for over-torque protection of the electric motor to turn off in the start-up stage the electric motor when the rotational speed variation is less than a rotational speed variation threshold; and to control the electric motor to be in an operation stage when the rotational speed of the electric motor is greater than the preset target rotational speed; and to control in the operation stage the electric motor in a control manner providing a stable output torque. to control the electric motor to be in a start-up stage when the rotational speed of the electric motor is less than or equal to a preset target rotational speed; and for over-torque protection of the electric motor to turn off in the start-up stage the electric motor when the rotational speed variation is less than a rotational speed variation threshold; and to control the electric motor to be in an operation stage when the rotational speed of the electric motor is greater than the preset target rotational speed; and to control in the operation stage the electric motor in a control manner providing a stable output torque. <EOS>