The characteristics of apparent defects in lining of horizontal section and inclined section of diversion tunnel are quite different under different stress conditions. Aiming at the problem that stress characteristics of different structural sections of tunnel affect the distribution of defects, an intelligent robot equipped with 3D laser scanner is used to collect data on apparent defects of tunnel. Based on the characteristics and rules of the inspection data of different structural sections, the mechanical mechanism of the defects in the upper flat section and the inclined section of the tunnel is studied, and the three-dimensional model of the tunnel is established by finite element software to analyze the stress and deformation characteristics of the upper flat section and the inclined section. The results show that the number of defects in the upper horizontal section of the diversion tunnel is obviously more than that in the inclined section, and the defects are mainly distributed in the vault. When the measured pressure coefficient of the surrounding rock is less than 1/3, the stress on the top of the lining structure in the upper flat section is greater than that on the waist and bottom of the arch, while the stress on the wall of the inclined section is smaller than that of the upper flat section due to the pressure component of the surrounding rock caused by the inclination Angle. The numerical simulation shows that the settlement at the top of the tunnel is obvious, and the pressure difference in the upper flat section caused by the disturbance of the surrounding rock is greater, which is in good agreement with the mechanism analysis of the inspection results. Keywords:diversion tunnel；inclined shaft section；apparent defect；mechanical mechanism