In order to solve diseases such as large deformation of initial support or roof caving that occurs frequently in the construction of shallow-buried large-span tunnels, the characteristics of large deformation and roof caving disaster were analyzed based on the tunnel in Baise City Guangxi Province. The PFC discrete element software was used to analyze the evolution of instability. The treatment technology of large deformation of tunnel primary support was put forward. The results show that, during the construction of shallow-buried large-span tunnel, it is easy to be affected by factors such as surrounding rock conditions and support strength, resulting in large deformation or collapse of surrounding rock. The deformation of surrounding rock can be effectively controlled by means of surface grouting reinforcement, temporary inverted arch and back pressure in tunnel. Security risks can be reduced by establishing management system, strengthening personnel training, setting up safety channels, arranging safety personnel, strengthening safety awareness, and establishing evaluation and early warning mechanisms. The research results can provide reference for the prevention and control of construction disasters in shallow buried large-span tunnel.