A three-dimensional reconstruction system for underwater lasers is proposed, which is composed of a camera, green linear laser and turntable. The three-dimensional reconstruction of the target area is realized by analyzing and processing the image scanned by the system. In the aspect of point cloud processing, this paper combines the alpha shape boundary extraction algorithm and Delaunay triangulation to realize the filtering and reconstruction of point clouds. Aiming at the problem of viewing angle error caused by light refraction on different media surfaces in the experiment, a refraction correction algorithm is proposed, and the error experiment is carried out with a standard ball of known size. The results show that at a working distance of 500-1200 mm, the system can restore the three-dimensional morphology of underwater target objects and regions, and the reconstruction error is less than 0.6 mm, which meets the design requirements and provides a new reference for underwater three-dimensional reconstruction technology.