A concise analytical method (extending coefficient) of coupling between two nonparallel waveguides is reported in this paper. By this method, a novel coupled equations are derived for two non-parallel waveguides. From this, the perfect analytic solutions between two nonparallel waveguides are obtained. In according with these analytic solutions, the propagation distance and spaces of input/output-guide ports and angle may be optimized for the nonparallel waveguide structures.