Abstract: The mid-wall of a multi-arch tunnel is an important loading component and has direct impact on tunnel safety and economy. In order to understand the mechanical behaviors of the mid-wall of a multi-arch loess tunnel,systematic test and analysis were conducted based on a multi-arch loess tunnel in northern Shaanxi province regarding contacting pressure on top and bottom of the middle-wall, axial force of anchor bolt in middle pilot heading and axial force of rebar meter at the middle-wall as well as internal force of the mid-wall using the steel wire transducer.The test results indicate that the pressure at the bottom of mid-wall approximately take a saddle shape, which is large on both sides and small in the middle and the pressure at the base is larger than the contacting pressure at the top of middle pilot heading; axial force of anchor bolt is small, peak axial force occurs at shallow-buried part of rock mass and axial force at the deep-buried part is about 10% of that in shallow-buried section, the support effect of anchor bolt at middle pilot heading is not obvious and anchor bolt can be canceled at this place; the axial force of rebar meter at middle-wall is increasing towards the bottom and it’s more sensitive to the force on the upper part of midwall compared with that on the lower part; the max. force of mid-wall occurs at the left lower side of mid-wall, and stress release of the right and left tubes has certain "rectification" effect on force of mid-wall but the mid-wall has always been affected by asymmetric pressure; the calculated max. axial force of mid-wall is about 583 kN, the max.bending moment is about 45 kN·m, the mid-wall is stable, the max. longitudinal torque is around 79 kN·m and the internal force is very complex.