A device for measuring the retraction value of a clamping piece comprises a fixed part and a movable part. The fixed part is composed of a fixed seat, a protective guide sleeve, a pressing cover and an end cover. The movable part is composed of a measurement adjustment seat, a sliding stretchable plate, a connecting plate, a plug and a piston sleeve. The piston sleeve is installed in the protective guide sleeve. The end cover and the pressing cover are each located at one end of the protective guide sleeve. The pressing cover compresses the piston sleeve in the initial position through a compressing spring. A micro self-recovery type displacement sensor is fixedly installed on the piston sleeve. An intelligent jack with the device for measuring the retraction value of the clamping piece comprises the device for measuring the retraction value of the clamping piece, a jack body and a computer control system. The fixed part of the device for measuring the retraction value of the clamping piece is fixedly connected with a connecting backing ring fixed at the front end of a piston of the jack body. The measurement adjustment seat of the movable part of the device is arranged on the surface of the tool clamping piece and stretches out and draws back along with the jack body overall, so that the retraction value of the clamping piece is measured in real time in the stretching process of the jack body, and the accurate value obtained through the sensor is transmitted to the computer control system connected with the sensor.