For the issue of workpiece size measurement, most of them use manual method to measure the size of workpiece, which is not only labor-intensive, but also prone to errors. In order to avoid this kind of situation, machine vision technology is designed to measure the size of the workpiece. Here, this paper uses Halcon image processing software to measure the height of the workpiece, uses binocular camera to collect the image of the workpiece, analyzes the working principle of binocular stereo vision, calibrates the camera, and puts forward a method of extracting saddle point to locate the workpiece, and uses plane vector to determine the height dimension of the workpiece, Results the height dimension of the workpiece was successfully measured to be 50.3mm. The experimental results show that after a series of binocular stereo vision processing methods, the height and size of the workpiece can be obtained, which not only improves the efficiency, but also has great practical value for the automatic production of the assembly line.