A photonic crystal coupling structure is designed by introducing two parallel single-mode defect waveguides with the spacing of one row coupling rods in the two-dimensional (2D) triangular lattice array. By modulating the refractive index of some coupling rods, an optical switch based on coupled heterostructure photonic-crystal waveguides is constructed. The coupling lengths for different refractive indices of coupling rods at different frequencies are calculated to determine optimal structural parameters for the switch by the plane-wave expansion method and the principle of directional coupling. The effect of variations in the refractive index of the coupling rods and the position effect of the heterostructure coupled waveguides on the signal output channel are analyzed by using finite different time domain method. The simulation results show that it is an effective way to realize the switch function by appropriately tuning the refractive index of some coupling rods. The influence of the random distribution of the heterostructure on the switch is modest, which may contribute to the research over new kinds of optical filters, directional couplers, wavelength division multiplexers, optical switches and other photonic devices.