Abstract: The Cosserat continuum theory considering the influence of deformation characteristic of media by coupled stress can reflect the bending deformation of the layered materials. The basic principle of the Cosserat continuum theory and its expanded constitutive model are introduced firstly, and the Mohr-Coulomb plastic yield criterion for the new model is deduced. Then the FEM program is written by use of Matlab system and applied to the stress analysis of the underground cavern in layered rock mass. The FEM program is proven to be effective, and the Cosserat expanded model which complements the parameter equivalent method is one of effective methods for solving interlayered rock mass question.