Based on the principle of resonant coupling between the ring cavity an d the line-defect waveguide of photonic crystals,a four-channel two-dimensional triangular lattice photonic crystal filter composed of a new ring cavity and a main waveguide is designed.The transmission characteristics of lig ht waves in the integrated structure are analyzed by using the plane wave expansion method and the finite-difference time-domain method,and the influence of the radius of the internal medium column in the annular filter is f urther discussed.The results show that the transmission efficiency of the new improved ring filter reaches about 80%.T hrough the experiment and selection of internal medium column radius R in 0.44~0.53R,its transmission efficiency is above 85%,and further select internal media column radius of 0.46R,0.47R,048R,0.52R made four channel filter,implements the wavelength is 1646.9nm,1647.7nm and 1648.5nm and 1652.3nm four channel WDM,its transmission ef ficiency is over 92%, half peak width is less than 6.0nm,high transmission efficiency is high,the f ilter narrow-band characteristic is good,suitable optical device integration.