The present application discloses a flexible clamping device. A sleeve is fixed on a base, an adjusting shaft is connected with a mandrel and the sleeve respectively, the mandrel is fixed on the upper end face of the adjusting shaft, and the bottom outer wall of the adjusting shaft is in small clearance fit with the inner wall of the sleeve; a lock screw is installed on the upper right side wall of the sleeve, a pinion is installed on the upper left side wall of the sleeve via a rotating shaft, saw teeth are provided on the side wall of a adjusting shaft, and the pinion can be engaged with the side teeth of the adjusting shaft.