Based on the temporal coupled-mode theory and the light-controlling characteristics of line-defect waveguides and point-defect resonant cavities， a two-channel filtering system composed of a main waveguide， two drop waveguides， two resonant cavities， and two reflecting cavities was designed using the two-dimensional square lattice photonic crystal. The band structures of the complete photonic crystal and the line-defect waveguide were calculated by the plane-wave expansion （PWE） method， and the modal distribution of the point-defect resonant cavity was analyzed. Using the Finite-Difference Time-Domain （FDTD） method， the transmission characteristics of the filtering system were investigated. The effects of linear variations in the distances from the reflector and reflection cavity to the reference plane of the resonant cavity on the system’s download efficiency were analyzed. Additionally， the variation patterns of transmittance peaks with these distance parameters were elucidated. Guided by the calculation results， the simulation design of the filtering system was implemented. The simulation results demonstrate that the filtering system can couple the optical signals with wavelengths of 1 561.2 nm and 1 570.5 nm into their respective drop waveguides with relatively high precision. The transmission efficiencies of them are 98.9% and 97.2%. The full width at half maximum （FWHM） values are 3.3 nm and 3.5 nm. The quality factors are 473 and 449， and the wavelength interval is Δλ=9.3 nm. The proposed filtering system exhibits a compact footprint of merely 20.88 μm×22.04 μm with a structurally simple configuration. Featuring a tunable operating wavelength and high compatibility with large-scale integration， this study can provide certain theoretical foundations and conceptual insights for the design of integrated optical circuits in optical communications.