In view of some industrial diameter measurement scenes where the camera cannot be installed on the end face to be measured, a cylindrical workpiece diameter measurement system is designed, which consists of three linear lasers, an image lens and an area array CMOS camera. It is placed on the ground, projectes and images obliquely. A measurement system is set up. The sub-pixel endpoint coordinates from the image are obtained. The calibration equation is substituted to solve the world coordinates, and the diameter to be measured through the geometric model is calculated. The experimental results show that the system can accurately measure the diameter of the workpiece near the designed value, and the measurement accuracy is within ±0.1 mm, which meets the high precision requirements of industrial measurement.