The force mode of primary support of tunnel on Menghua Railway under construction is studied; and the field measurement is carried out on the displacement around tunnel and the force state of primary support. The results show that: 1) The primary support is generally compressed; and the structure is under slightly eccentricity pressing condition. 2) The convergence displacement around the tunnel is small; and the deformation of the tunnel towards the clearance side is consistent with the force mode of the primary support under general compression. 3) The displacement around the tunnel, the axial force of the bolt and the force state of primary support are not accordance with force mode under loose stress of slump arch, but in line with the deformation stress due to the interaction between surrounding rock and support. 4) The grid steel frame contributes little to stress and shear capacity of the structure; the shear strength of oblique section of primary support is mainly controlled by concrete; and the effect of the grid steel frame is only to provide postpeak toughness after concrete cracking.