A novel concise analytical method of the coupling among three nonparallel waveguidesextended coupling coefficient method is reported. The change of nonparallel-waveguide geometric shape is directly translated into the one of the interval among the parallel waveguides in the coupling coefficient, in other words, the coupling coefficient is extended technologically, the change of the distance among parallel waveguides is included in coupling equations by exponent, and the novel coupling-mode equations are derived for three nonparallel waveguides. These coupling-mode equations include all information such as the amplitude and phase of the nonparallel waveguides, the distances among input ports and the angle, the propagation distance and the power translating with these parameters, etc.. Using the skilled mathematic conversion, the perfect analytical solutions are obtained by solving the equations. The coupling among three nonparallel waveguides is analyed and discussed for symmetrical and asymmetrical initial conditions. In accordance with these analytic solutions, the optimum parameters can be presented for the nonparallel waveguide structures.