The invention relates to a precise adjusting device for a rotating angle of a servo mechanism, belongs to the technical field of a rotary angle adjusting device of the servo mechanism, and aims to provide a rotary driving device capable of precisely adjusting the rotary angle of the servo mechanism. According to the technical scheme, a support is vertically fixed on the top of a shell of the servomechanism, and a shaft seat is fixed on the upper portion of the support; one end of a floating pin roll is a cylindrical end connected to the shaft seat while the other end of the floating pin rollis a square end connected to an adjusting screw; one end of the adjusting screw is connected to a hand wheel while the other end of the adjusting screw is a semi-spherical end connected to one end ofa rotary shaft, and the other end of the rotary shaft is connected to a rotary part of the servo mechanism on the side face of the shell of the servo mechanism. The precise adjusting device provided by the invention is applied to adjusting the rotating angle of the servo motor.