The invention relates to a cable sheath tensile length measuring device and a cable sheath tensile length measuring method based on machine vision. The measuring device comprises a tension sensor, a tension transmission mechanism, and a servo motor, and is characterized by further comprising an upper computer, an embedded controller, and an industrial camera, wherein the embedded controller, the industrial camera, the tension sensor, the tension transmission mechanism and the servo motor constitute a lower computer. The embedded controller comprises a touch screen display module, a tension sensor processing module, a camera image processing module, a data processing module, and an upper computer communication module, wherein the input end of the touch screen display module, the output end of the camera image processing module and the input end of the upper computer communication module are connected with the data processing module, the data processing module is connected with the tension sensor through the tension sensor processing module, the input end of the camera image processing module is connected with the industrial camera through a USB cable, and the upper computer communication module is connected with the upper computer through a network cable.