Abstract: The loess in Lanzhou is characterized by severe collapsibility, high compressibility and dynamic vulner? ability due to its loose texture, large void ratio and low strength, and it′ s easy to cause failures at tunnel floor and building foundation whenever the positive pressure or pore water pressure increase. Aiming at the deformation of a large-section loess tunnel in Lanzhou, reinforcement is conducted by the lime-soil compaction pile, and a three-dimensional numerical method is adopted to study the characteristics of deformations and mechanical behaviors before and after reinforcement with lime-soil compaction piles. The results show that before reinforcement with limesoil piles the heaving occurs and gradually increases along with the direction of excavation, subsidence occurs at arch spring, the maximum displacement occurs at the center of tunnel bottom; after reinforcement with lime-soil piles, the pile axial force, pile stress and pile displacement are small on both sides and large in the middle in horizontal direction, and they increase gradually along with the excavation direction, the piles bear most of the load produced by tunnel excavation, and the force and deformation at tunnel bottom decrease, and the displacement at tun? nel floor is reduced by 32%-34.4%, which shows the lime-soil compaction pile can improve the bearing capacity and resistance to deformation at tunnel bottom of the loess tunnel.