To solving the engineering problems of tunneling in backfill soils, the shallow buried concealed excavation of the northern line of the Zengjiayan Bridge Tunnel Project in Chongqing has been taken as the relying project and numerical analysis and monitoring have been used to study on deformation characteristics of surrounding rock in small clearance tunnel excavation in backfill soil layer. The result of this study reveals that: firstly, during the excavation the maximum surface settlement will move from the top of the advance tunnel to the top of the intermediate rock pillar. Secondly, the surrounding rock deformation pattern of the backward tunnel could be described as: predeformation-sharp deformation- deformation convergence, and the surrounding rock deformation pattern of the advance tunnel could be described as: predeformation-sharp deformation- first deformation convergence- additional deformation- final deformation convergence. Thirdly, the excavation of the advance tunnel will lead to the predeformation in vault, arch and the side wall of the backward tunnel, and the excavation of the backward tunnel will lead to the additional deformation in the same places of the advance tunnel. The conclusion of this study is consistent with the existing research and can provide reference for similar projects.