Lixie Tunnel is locted in Ningbo, China. which is a multi-arch tunnel of bidirectional four roadways on Xiangshangang port bridge road. There are complex geologic conditions, broken surrounding rock and obvious unsymmetrical pressure phenomenon. The surrounding rock deformation of the left hole of portal section was suddenly becoming increased after heavy rain erosion, accelerated rate of deformation, and collapse appeared. Based on the analysis of the objective and subjective of collapse reason, the brush slope treatment , long pipe shed methods and sprayed concrete were designed for reinforcement tretment, at the same time , a new monitoring section was designed in the collapse section of the left hole to observe convergence displacement, vault subsidence and surface subsidence, and treatment construction process of tunnel collapse section was simulated by FLAC. The comparative results show that the monitoring measurement and numerical simulated results is same, the surrounding rock of portal section is basically stabilized after treatment and get good results. It provide a reference for similar projects.