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Debris flow accumulation has the characteristics of loose and broken, low strength, poor stability and so on. When the tunnel passes through the debris flow accumulation area, it is easy to bring major safety hazards to the construction site. Based on the engineering background of Gangou tunnel crossing debris flow accumulation area in the fourth bid of Jiumian expressway, this paper establishes a numerical calculation model, studies the large deformation characteristics of tunnel surrounding rock in debris flow area, determines the reasonable reinforcement range of tunnel surrounding rock, and puts forward the comprehensive control technology of tunnel passing through debris flow accumulation body combining surface stability and underground reinforcement based on simulation results and field experience. The numerical results show that the deformation of surrounding rock and ground surface can be effectively controlled. The rationality of the proposed control measures is verified by field monitoring, which provides a reference for surrounding rock control of tunnel under type conditions.