With regard to the coupling characteristics of multiple kinds of bending waveguides of NRD waveguides with different curvature radii, a novel and general analysis method was presented. When the coupling structures become the asymmetric (coupling of a straight waveguide with a bending one) or the symmetric (coupling between two bending waveguides of the same curvature radii) structures, the new method can be simplified, respectively, to be in full accordance with the reported results. Experiments were done at 60GHz for the frequency responses and the bandwidth characteristics of couplers by using bending waveguides with various curvature radii. And the generality and validity of the method were verified.