Abstract: In order to solve the construction problems of the Yuelongmen Tunnel on the Chengdu-Lanzhou Railway, in-depth research is carried out in terms of formation background, cause mechanism, characteristic laws and prevention countermeasures of major engineering problems such as active fault, karst water inflow, harmful gases, large deformation and high ground temperature. The results show that the regional geological characteristics of the complex western mountainous area with strong earthquakes, where the Yuelongmen Tunnel is located, are remarkable, and the regional geological research and test effort should be strengthened. During construction in active fault areas, tunnel body should be verified to understand the nature of the fault and the differences between the renovations of hanging wall and footwall. To solve complex geological problems, it is necessary to strengthen regional geological evolution analysis, divide geological environmental units, and form a regional engineering geological concept.