For Liujiazhuang railway tunnel of Shanghai-Kunming through the coal strata in construction of large deformation phenomenon, based on theoretical analysis, numerical simulation and field monitoring method, this study investigates the causes of significant deformation in tunnels, focusing on the initial locations of this deformation. It examines the impact of stress states on unit cells aligned with the inclined direction of a coal seam and explores the relationship between tunnel depth and horizontal distance in tilted strata. Additionally, the research analyses the stress and deformation experienced by the element body and the primary support structures in an inclined coal seam. The result showed that the stress state of the coal element above the palm face increases with the horizontal distance between the palm face and the bottom of the inclined coal seam, and the rock mass is subjected to three deformation stages including extrusion, compression shear and shear slip. The large deformation of surrounding rock and the failure of primary support structure both occur in the early stage of shear slip stage, so shotcreting to palm face, grouting reinforcement to coal seam up the palm face and strengthening the stiffness of primary support should be taken to prevent the large deformation of the tunnel in the stage of compression and shear deformation combined with the field monitoring data.