According to the engineering geological conditions of some tunnel,selecting the typical profiles,the changes of displacement and stress of tunnel’s surrounding rock caused by excavation when there was or was not karst cave was simulated using three-dimensional finite element method,and the influence of karst cave on stability of tunnel was evaluated.It was pointed out that if karst cave is closer to tunnel’s roof,tunnel excavation may lead to the fracture and collapse of the roof,thereby resulting in such geological hazards as silt and water inrush.