This paper presents the design of an eight-channel dense wavelength division multiplexer based on a photonic crystal AAH cavity. The model is established and transmission performance is analyzed using coupled mode theory, and the design is validated through three-dimensional finite-difference time-domain simulations. The simulation results demonstrate that the device can achieve dense wavelength division multiplexing functionality with a channel spacing of 0.8nm at operating wavelengths of 1558.4nm, 1557.6nm, 1556.8nm, 1556.0nm, 1555.2nm, 1554.4nm, 1553.6nm, and 1552.8nm. The device exhibits a minimum insertion loss of 0.22dB and a minimum channel crosstalk of -61dB. The linewidth is uniformly 0.2nm, and the size of the eight-channel device is only. This device features low loss, low crosstalk, and narrow linewidth, with a simple structure that can be easily expanded to accommodate more channels, making it suitable for high-speed, high-capacity optical communication systems.