Aiming at the problems of low efficiency, low accuracy and inconsistent measurement in the manual measurement of the groove size of the inner wire joint in the actual industrial inspection, a groove size measurement system of the inner wire joint based on machine vision is developed. Firstly, the groove position is located by morphology, and then the edge of the groove is accurately found by bilateral filtering combined with Roberts operator, Finally, the edge is fitted into straight line segments by the least square method, the minimum distance between straight line segments is calculated by Halcon image processing software, and the measurement results are displayed by c# combining Halcon library. The experimental results show that the measurement accuracy of the system is ± 0.01mm, the detection accuracy of the measurement system is 98.73%, the missed detection rate is 0, and the over detection rate is 1.27%; In terms of detection time, the average time for detecting a workpiece is 0.37s. The system has high measurement accuracy, stable measurement and fast operation speed, so it can effectively replace the manual measurement in industrial detection.