Based on the resonant coupling principle between the defect mode of a ring resonator and the line-defect waveguide,a four-channel Wavelength Division Multiplexing(WDM) system was designed by using the 2D triangular lattice photonic crystal.This system was composed of a line-defect waveguide,ring resonators and 60° bend waveguides.The band structure of the line waveguide was investigated by the plane-wave expansion method.The transmission characteristics of light wave with different frequencies in the system were simulated by the finite difference time domain method,the effects of factors on output efficiency and quality factor were analyzed and the system was improved.The analysis shows that the resonance frequencies depend on the radius of the dielectric rods.It is demonstrated that the transmission efficiencies of the system is improved greatly by changing the shapes of dielectric rods in the coupling region and adding the reflection dielectric rods at the end of bus waveguide.The numerical results indicate that the system has the ability to achieve the WDM for different wavelengths,and the transmission efficiencies of all the resonance wavelengths are still above 90%.The system is a simple structure and easy to be fabricated and processed.Moreorer,it has a smaller size,and could be large-scale integration.