Research conclusions:To the tunnel with soft － weak surrounding rock，the step excavation method should be adopted，the preliminary bracing should be conducted as early as possible and the closure to form a loop should be done as early as possible to improve the loading structure of the surrounding rock． The coordination between the design and construction should be strengthened． The displacement during construction should be monitored to know the change regulation of the displacement，so the design parameters can be adjusted dynamically and the time of laying the secondary lining can be adjusted．If necessary，the inverted arch and the secondary lining should be done immediately to ensure the security of the tunnel construction．