Deeply buried tunnels usually lie in high stress fields, in which horizontal stresses are not uniform and far larger than vertical stresses, and tunnel stability is dominated by the original in-situ stresses. With three-dimensional nonlinear finite element method, the effects of tunnel in axis orientation on the displacement and stability of two types of surrounding rocks are studied systematically for two parallel tunnels and single tunnel. The tunnel lies in different kinds of rocks and in such different original stress fields that the maximum horizontal principal stress is parallel to or perpendicular to the axis or the stress field is gravity. The numerical analysis results show that the plastic zones occur in the side wall of the tunnel mostly when the horizontal maximum principal stress is parallel to the tunnel axis, while the plastic zones distribute in the top and bottom of the tunnel when the horizontal maximum principal stress is perpendicular to the tunnel axis. It is concluded that the instruction of tunnel axis should beparallel to horizontal maximum principal stress regulated by the “specification for design of hydraulic tunnel” is not available for the stability of tunnel always.