Aiming at the problem that the diameter measurement system of cylinder parts is complicated and the error is large, a diameter measurement method based on double line structured light vision system is proposed in this paper. In this method, two non-cross laser lines are irradiated on the surface of the workpiece, the curvature information of the laser fringe is effectively used to extract the subpixel center point accurately, and the normal deviation threshold is set to eliminate the abnormal point. Through biplane calibration, the equation of the vertical plane of the center axis is derived to correct the error of non-vertical irradiation of the laser line. Finally, the effective points are fitted on the vertical plane, and the average value of the multi-angle fitting data is taken as the diameter measurement value. The experimental results show that compared with the local laser scanning method, the measurement accuracy of the proposed method is improved by about 30 μm, and the average measurement error of the diameter of the cylindrical workpiece within 200mm diameter is less than 17 μm, which improves the detection accuracy and loosens the measurement system requirements.