Research conclusions: The Chahe tunnel was a typical case that the tunnel became and developed into a landslide tunnel due to the joint effects of the unsymmetrical pressures of terrain and the geological structure. The special terrain and the slope geological structures and the geological characteristics of each soil layer made the slope easily to be pressured unsymmetrically. The soft and weak sliding zone formed along the bedding surface and the high-angle fault surface were the internal factors of the landslide formation. The river erosion, the rain infiltration and especially the intermittent declining movement of the hanging side of the F1 high-angle normal fault caused by the structure movement and seismic action were the important external triggering factors for the formation and development of landslide. The respected treatment effect can be achieved by doing the comprehensive treatments according to the investigation conclusions and suggestions.