Abstract: Soft behaviors always occur in rock and soil engineering, however, the mesh-dependence will be caused when traditional elastoplastic finite element method is applied in shear bands problems with soft behavior. This paper introduces the couple stress elastoplastic theory, and develops flow finite element frame satisfying Drucker-Prager yield criterion. The developed finite element frame is modeled using RCT9+RT9 element passing C0―1 patch test, and finally be added to finite element software ABAQUS through user subroutines UEL. Numerical results show that couple stress theory can eliminate the deficiency of mesh-dependence, and finally is demonstrated to be effective in rock and soil softening problems.