In order to solve the problem of large deformation of shallow soft rock tunnel during excavation, this paper relies on the tunnel project under construction, analyzes the deformation and failure characteristics of the initial support of the tunnel, and uses numerical simulation software to analyze the cause of the large deformation and propose a reasonable deformation control measures. The results show that the surrounding rock at the shallow buried section of the cave entrance is affected by excavation disturbances and groundwater. The surrounding rock has a large amount of deformation and the longitudinal deformation is irregularly distributed; the initial deformation of the excavation is fast and the deformation rate is large, up to 38.4mm/d; the deformation lasts for a long time , The deformation can reach 10.2mm/d in the later stage of deformation; the deformation mainly occurs in the upper and middle step excavation stage, about 70%; the initial support stress is too large, and the excessive development of the plastic zone is the main reason for the large deformation of the tunnel. According to on-site monitoring data and numerical simulation results, comprehensive treatment measures are proposed to optimize construction methods, improve support parameters, carry out precipitation in the cave, and increase the amount of reserved deformation. The research results can provide references for the prevention and treatment of large deformations similar to soft rock tunnels.