In order to learn the influence of the halfdeep cave in the threebench excavation on the stability of the highway tunnel, the influence of locations and dimensions of caverns on surrounding rock deformation of primary support structure stress characteristics of Lidong Tunnel is studied by model test and theoretical analysis. The results show that: (1) The timehistory curves of settlement of the tunnel crown and the surrounding convergence show a Sshaped variation under different locations and dimensions of caverns, which can divided into 4 stages, i.e. initial slowly growing stage, mutation stage, slowly growing stage, and stable stage. (2) The extrusion of the working face changing with the internal pressure of the cavern shows an “exponential” growth, with obvious internal pressure abrupt points; the internal pressure of the cavern is the lowest at the position of the invert, and the internal pressure of the cavern is the highest at the position of the sidewall; the smaller the karst hole, the higher the internal pressure of the mutation. (3) The position of the cavern has a great influence on the support structure on the near side, and the influence on the support structure on the far side gets smaller; by changing the position of the cavern, the axial force on the left side of the tunnel steel arch shows a certain fluctuation, while the axial force on the right side tends to be stable.