Abstract: According to the gradual deformation principle of surrounding rock mass under the in-situ three-dimensional stress condition after tunnel excavation, the deformation characteristics of the rock mass was analyzed and the rock mass was zoned rationally. It is assumed that the rock mass is governed by the twin shear stress three-parameter criterion in the unified strength theory. The analyti-cal solutions of some factors were deduced under axisymmetric loads, including the stress field, strain field, support force and plastic radius in the plastic zone. The case analysis result shows that this selected strength theory matches to the actual strength characteristics of the rock mass due to taking the effect of intermediate principal stress into account.