In order to solve the problem of all-optical communication network capacity and spectral efficiency, a two-cavity six-channel Wavelength Division Multiplexer (WDM) based on the coupling characteristics of point-defect cavity and line-defect waveguide of Two-Dimensional (2-D) photonic crystal is proposed in this paper. 2-D finite-difference time-domain method is used to analyze the performance parameters. Considering the influence of relative refractive index, the coupling mode of double resonators and single straight waveguide is selected to achieve the wavelength division multiplexing of 1 451, 1 487, 1 557, 1 658, 1 440 and 1 604 nm. The results show that the multiplexer has a spectral coverage of up to 218 nm, transmission efficiency of each channel higher than 91%, the insertion loss less than 0.43 dB, the cross-talk between channels less than -9.2 dB, and the size of only 13.56 μm×19.21 μm. It is very useful for coarse wavelength division multiplexing in optical communication systems, which also has reference significance for dense wavelength division multiplexing.