Abstract: When the tunnel passes through the area of weak surrounding rock with high geostress and rich water, it is prone to all sorts of adversities, such as collapses, initial support structure intrusion, distortion and detachment of steel frames. In view of this problem, Muzhailing highway tunnel of the Weiyuan-Wudu Expressway is taken as the study object, and the finite difference method software FLAC^3D was used to establish the numerical simulation model of the tunnel with two construction methods under different water contents, namely, the double-side heading method and three-level seven-step excavation method. The distribution and development of surrounding rock pressure, vertical and horizontal displacement and plastic zone with the increase of the water content were analyzed and discussed under the two construction methods. The results show that with the increase of the water content, the strength of the carbonaceous slate decreased, so did the self-stability of the surrounding rock, which in turn affected the stability of the tunnel. After the excavation of the upper level of the tunnel, the settlement and convergence deformation of the key parts of each monitoring section in the soft surrounding rock section accelerated and expanded. With the application of initial support, the settlement and convergence deformation speed gradually eased, and stabilized at the distance of 50 meters away from the tunnel face.