The maintenance of railway tunnel linings necessitates regular inspections due to potential safety hazards arising from deformation during service. While traditional manual inspection methods employing total stations offer high accuracy, they suffer from inefficiency due to frequent station changes, rendering them unsuitable for China's extensive railway tunnel network characterized by long mileage and short inspection windows. In order to solve the problem of intelligent, rapid and high-precision detection of structural deformation in railway tunnels, this study proposes a method for detecting structural deformation of railway tunnels based on mobile laser scanning. The TMMS inspection vehicle equipped with Z + F PROFILER 9012 laser scanner is utilized to carry out the point cloud data acquisition work in a railway tunnel with a length of 573 m in Yunnan Province, and the solution of the geometric deformation of the tunnel structure is carried out through the steps of tunnel section extraction, point cloud data noise reduction, and ellipse fitting. The research outcomes furnish theoretical support and practical guidance for enhancing the intelligent inspection of railway tunnel lining structure deformation.