A photonic crystal coupling structure is designed by introducing two parallel single mode defect waveguides with one row coupling rods in between them in the two-dimensional (2D) triangular lattice array. Based on the analysis of coupling and decoupling property of the coupled photonic crystal waveguides, it is known that different normalized frequencies correspond to different coupling lengths. The coupling lengths for coupled waveguides at different frequencies are calculated to design a new super-tiny photonic crystal three-wavelength power splitter by the plane wave expansion method and the principle of directional coupling. The effect of splitting the beam with normalized frequencies of 0.369, 0.394 and 0.435 are obtained. The function of the power splitter is analyzed by using finite different time domain method. The simulation results show that it has a good splitting beam effect. The result should contribute to the research over new kinds of optical filters, directional couplers, wavelength division multiplexers, polarization beam splitter, optical switches and other photonic devices.