Control method and control system for electric tool, and electric tool

A control method for an electric tool. The control method comprises the following steps: detecting a parameter x that is used for expressing an output shaft load of a motor; and determining that the output shaft load is reduced to be equal to or less than a preset load according to that the parameter x meets a preset condition, and then changing the rotating speed of the motor. Also disclosed are a control system and an electric tool that applies the control system. By means of the control method and the control system for the electric tool, a nut and a bolt can be loosened without being separated, the nut and the bolt can be separated manually by a user as required, and the requirement on the special working condition of loosening the nut only by the user is met.