An optical switching model was established based on the transmission characteristics of electromagnetic wave in the photonic-crystal coupling waveguides. The coupling length was calculated when the refractive index of the coupling dielectric rods is in different values by using the coupling mode theory and plane wave expansion method. Using finite-difference time-domain method, the light wave output condition was analyzed as refractive index of dielectric rods equals to 3 and 3.4, and the effect of position of heterostructure to the optical switching functions was also analyzed. The result shows that the function of optical switching changes when the dielectric rods refractive index is 3.4, but the position of heterostructure doesn’t change the optical switch function. These properties can be used in the design of optical switches more flexibility in practice.