A rotation speed control method for impact type fastening tools has a presetting step and a dynamic control step. The presetting step includes setting a plurality of working positions, and setting a PWM signal with a larger duty cycle as a driving signal in a period after energization so that a motor can rotate at a higher speed and improve work efficiency. When a main controller judges, according to feedback, that the operation enters an impact phase and torsion control is needed to reduce rotation speed, the main controller makes adjustment by driving the motor with a PWM signal with a lower duty cycle corresponding to a working position currently set by the user. The control method improves work efficiency, and meet the user's need of driving a fastener with a higher rotation speed at an early stage of operation. In the torsion control phase, the method according to the present invention can automatically use a suitable torsion to drive the fastener to better meet the user's needs in operation and enable the user to obtain an excellent experience of use.