Based on the resonant coupling principle between the photonic crystal ring cavity and the waveguide,a dual-function device of a six-port two-dimensional photonic crystal circular lattice with square arrangement composed of ring defects and line defects was designed.The transmission characteristics of the two-dimensional photonic crystal device were analyzed using the plane wave expansion method (PWEM) and finite-difference time-domain method (FDTD),and the transmission characteristics curve and light field distribution were obtained.Then,the influence of the inner diameter of the central column of the ring cavity and the radius of the dielectric column in the coupling region on the filtering efficiency and transmission rate of the output port was discussed.The results show that by adjusting the parameters of the center columns of the ring cavity and the dielectric columns in the coupling region,the device can simultaneously achieve good filtering and beam splitting functions.For input light waves with wavelengths of 1.510 μm and 1.515 μm,the device mainly has a filtering function,with filtering efficiencies of close to 99.95% and 93.27%,respectively.For input light waves with a wavelength of 1.490 μm,the device mainly has a beam splitting function,with a maximum transmission rate of 99.74%.