Construction process of mountain tunnel often encounters tunnel collapse. The causes of tunnel vault collapse and the effectiveness of reinforcement measures are studied from the aspects of rock layer distribution, rain erosion etc. The surrounding rock displacement of tunnel section near collapsed zone before and after reinforcement and the supporting structure stress are monitored. The result shows that the reinforcement measure of tunnel vault is practicable and the surrounding rock deformation and the structure stress are well controlled. In addition, FLAC3D simulation analysis was applied to tunnel collapse zone, and the obtained result is basically consistent with the field monitoring result. It indicates that the reinforcement measures are effect on the treatment of tunnel collapse.