Abstract: The Gaoligong mountain tunnel, characterized by its special geographic location and complicated geologi? cal conditions, is the longest railway tunnel under construction in China. The key points and difficulties that might be encountered during TBM tunnel construction are analyzed, including a high temperature of around 50℃, large deformation of the soft rock with a length of 3,185 m, an estimated maximum water inflow of 1.92 × 105 m3/d, a long seriously fractured section with 2,260 m in length, construction risk management for a tunnel of risk grade I and longdistance ventilation control. Key construction techniques are studied, such as high ground temperature prevention,controlling large deformation for soft rock, water inflow treatment and TBM construction in an unfavorable geological section of a fault fracture zone.