The rapid acquisition of 3D surface information and measurement of dimensions of workpieces online in the flow production lineis strongly required in the current intelligent upgrading process of manufacturing industries such as roll forming. The speckle projection based 3D reconstruction method can reconstruct the 3D data of object surface only by using a single object speckle image, which has certain advantages in the rapid measurement of workpieces online. In this paper, on the basis of optimizing the time-consuming corresponding point search algorithm in speckle 3D reconstruction, a rapid 3D measurement system for online workpiece measurement that is suitable for the roll forming production line is developed. The experimental results show that the system has a fast 3D data reconstruction speed, and the measurement error is within 0.035 mm, which can meet the requirements of rapid online measurement of 3D structural dimensions of rolled parts.