Abstract: To ensure the safe operation of railway trains, regular tunnel clearance inspection is required to acquire the minimum cross-sectional profile. However, mainstream inspection methods suffered from drawbacks including low inspection efficiency, heavy manual intervention, complicated data processing and high equipment costs. For this reason, this paper proposed a rapid inspection and three-dimensional (3D) visualization scheme for railway tunnel clearance based on laser line imaging. The scheme equipped inspection trains with Charge Coupled Device (CCD) cameras and laser transmitters to capture laser images of tunnel inner walls. It extracted feature information via image processing techniques, calculated tunnel clearances and determined clearance cross-sections by combining calibration files, and finally realized 3D tunnel visualization relying on the Matplotlib library. The verification experiments were conducted at an average speed of 106 km/h. Experimental results indicate that the proposed scheme achieved inspection accuracy within ±5 mm. This scheme significantly cuts manual workload, meets the practical demands of high-speed and high-precision railway tunnel clearance inspection as well as stereoscopic visualization, and delivers reliable data support for tunnel maintenance work.