In order to realize the efficient processing of optical information and the high integration of optical devices, according to the principle of resonant coupling between the ring cavity and the waveguide of a photonic crystal (PC), in this paper, we design a novel four-channel filter consisting of a point-defect resonator, a triangular ring resonator and a line defect waveguide and a reflective heterojunction based on a two-dimensional triangular lattice photonic crystal. The band maps of intact photonic crystals and line defect waveguides are obtained by plane wave expansion method (PWEM). The calculated results show that the reflected heterojunction has obvious effect on improving the filtering efficiency. Using the finite-difference time-domain method (FDTD), the filtering efficiency of the four-channel filter at 1.456 μm, 1.493 μm, 1.422 μm and 1.476 μm is simulated. The simulation results show that the filtering efficiency of the four-channel filter is above 99.84%, realizing the high efficiency filter output by adjusting parameters, such as the center medium column radius of the resonator. Moreover, the maximum insertion loss of each channel of the filter is only 0.009 dB, full width at half maximum less than 7.2 nm, and quality factor greater than 207. The four-channel filter designed in this paper achieves narrowband filtering and good performance parameters, with good applicability and generalizability in optical communication applications.