As a three-dimensional （3D） imaging technology， laser line scanning has been widely used in underwater target detection and topographic mapping. In this study， a set of underwater laser line scanning experimental equipment is constructed， and images obtained using a calibrated laser line scanning device are processed via laser strip extraction， feature extraction， and matching； subsequently， 3D reconstruction is performed. To mitigate the interference of underwater scattering particles， the light strip extraction algorithm is used， where the single channel threshold and gray center methods are combined to improve the accuracy of light strip extraction. Consequently， a higher robustness is achieved compared with that afforded by other light strip center extraction algorithms. In terms of feature extraction and matching， an image-based triangular displacement estimation method for system positioning and pose correction is proposed herein. This method applies the principle of line-structured light triangulation to estimate the scene depth， matches feature points to estimate system displacement， and fuses point cloud data to complete pose correction. We performed a standard ball accuracy test in a laboratory using a self-developed line scanning system， and the error can be controlled below 1 mm within a distance of 800–2500 mm. In 2019 and 2020， we performed 3D imaging tests of deep-sea seabed terrains with an ROV using the abovementioned system. The tests successfully validated the pose correction method of the proposed triangular displacement method in a sloped seabed sand area， and further tests were performed on the seabed terrain under different conditions. The results demonstrate that the corrected laser line scanning imaging device can perform imaging rapidly and accurately with a high degree of morphology reduction.