In the present paper， based on the coupling principle of photonic crystal resonator， a six-channel wavelength division multiplexer is designed by combining ring cavity with micro cavity structure. By using the plane wave expansion method， the relationship between the band gap of photonic crystal and the radius of dielectric cylinder is studied when the lattice constant is 0.55 μm， and the band structure is obtained. The influence of the resonator structure on the wavelength is analyzed by using the finite difference time domain method. The transmission characteristic curve and electric field distribution of the resonator structure are obtained. Six-channel wavelength division multiplexing with wavelengths of 1.3298，1.4316，1.4419，1.5564，1.5966，1.6191 μm is realized. Experimental results show that the device can select the frequency by adjusting the radius of the dielectric column inside and outside the microcavity， reduce the crosstalk by increasing the micro cavity structure of the reflection point， and improve the output efficiency by changing the radius of the dielectric column at the output edge. A channel with a transmittance of more than 90% and an average bandwidth of 9 nm is finally realized， and the crosstalk between channels is small and the narrow band characteristic is good. The size of the device is only 13.4 μm×17.6 μm， which is conducive to optical device integration and has potential application value.