In order to realize the function of wavelength division multiplexer with compact structure and high transmissivity, a high efficient three-channel wavelength division demultiplexer based on the energy band characteristics of photonic crystal is presented. Based on the plane wave expansion method(PWE), the propagation characteristics of photonic crystals are analyzed and the band gap of photonic crystals is given. The finite element method(FEM) is used to optimize the structure parameters of the device and the transmission spectrums of different ports are given. The experiment results show that the proposed device is able to drop three channels at resonance wavelength of 1537.8 nm, 1543.7 nm, 1548.7 nm. The transmission of output ports both reach 90%, the average channel spacing is about 5.5 nm, and the average value of the crosstalk between output channels is about -27 dB. Besides, it has high coupling efficiency, good wavelength selectivity, low value of channel spacing and crosstalk. At the same time, the wavelength adjustment method is simple and easy to integrate.