Shear stress distribution in anchorage interface of anchor is the attention points of anchor design. It directly affects anchoring effect. Shear stress in anchorage interface will cause larger strain gradient in rock and soil near anchorage interface. But the strain gradient is not considered in classical elastic theory which is used to analysis shear stress in anchorage interface. Bending curvature is introduced into couple stress theory which considers the effect on the deformation characteristics of the bending. The finite element calculation model for plane strain problem was build up based on couple stress theory. For tensile-type anchor，shear stress in anchorage interface and the boundary layer effect near anchorage interface and scale effect of couple stress were studied. The results of couple stress theory are compared with the results of classical elasticity theory. The results show that the shear stress and shear strain near anchorage interface in couple stress theory are smaller than that in classical theory，especially at the peak of shear stress. The shear stress on interface is not continuous. But shear strain abrupt change on interface has been improved; and a transition region appears near the interface. The characteristic length decreases; transition region becomes smaller; but strain gradient becomes larger. The influence on shear stress distribution in anchorage interface of the second shear modulus is not obvious.