The rock surfaces of tunnel excavated by the Tunnel Boring Machine (TBM) have various rough characteristics, which is closely related to the load transmission, the direction of excavation, and the wear of cutterhead when the boots of TBM is put on it directly. In this paper, the description on the 3D isotropic fractal rough surfaces of tunnel was calculated by using the modified W-M function. The normal contact stiffness models were established considering the failure of rocks when it underwent compressive loads applied by the boots of shield machines. The normal contact stiffness behavior was investigated considering the variable loads, mechanical behavior of rocks, and the surface roughness. The results show the normal contact stiffness is dependent on the failure of rocks. When the load remains unchanged, the contact stiffness of the parts of failure rocks supporting loads is smaller than those. It  decreases when rock failure occures on the contacting surface. The contact stiffness decreases with the increase of the surface roughness. When elastic modulus remains unchanged, the contact stiffness increases as the hardness increases. When the hardness remains unchanged, the contact stiffness increases as the elastic modulus decreases.