This paper focuses on the perception of underwater optical image information and designs an underwater line laser ranging system based on the point-to-point projection transformation capability of the homography matrix. The research addresses several issues, including the establishment of the homography transformation model, the correction of exposure images acquired by the camera, and the impact of the material properties of the objects on measurement accuracy. Firstly, the mathematical model of single-stress matrix ranging is established and the single-stress matrix is obtained by the LM algorithm. Next, to address potential exposure issues in the images captured by the camera in the laser rangefinder, image preprocessing is performed to correct exposure, ensuring measurement accuracy for underwater objects. Finally, in actual underwater scenarios, measurements were taken at four different distances using the laser rangefinder on a metal target object. The test results validate the feasibility of the proposed laser ranging solution based on the homography matrix.