In order to explore the influence of horizontal jet grouting arch shed defects on its pre-supporting effect， based on the actual project， a scale model test was designed to explore the deformation of arch shed and the change law of stratum settlement under different pile core occlusion distances. PLAXIS 3D finite element software is used to simulate tunnel excavation， and the influence of pile defects on the deformation trend and reinforcement effect of arch shed is explored. The model test results show that the larger the interlocking distance of the arch shed pile core， the larger the corresponding surface settlement and deflection. When the interlocking distance increases by 50 %， the surface settlement and deflection increase by 22 % and 33 %， respectively. The numerical analysis results show that the decrease of the occlusal area of the arch shed and the increase of the permeability coefficient of the stratum will aggravate the extrusion deformation of the tunnel face. When the occlusal area decreases to 25 %， the deformation increases by 78.77 %. The groundwater will drive the surrounding soil to infiltrate into the tunnel face from the defect. At this time， the arch shed appears stress concentration at the edge of the defect， and the maximum compressive stress increases by 110 %. The maximum principal stress at the defect changes from compressive stress to tensile stress， and the pre-support effect will be greatly reduced. Therefore， the quality of the pile core should be strictly controlled when the pile is formed in the project.