In this work, an eight-channel Dense Wavelength Division Multiplexing (DWDM) demultiplexer is designed with a 2D Photonic Crystal (PC) Triangular lattice. The proposed demultiplexer consists of a centre bus waveguide, an isosceles trapezium resonant cavity, and an eight circular ring cavity (CR1, CR2, CR3, CR4, CR5, CR6, CR7, and CR8). The point defect resonant cavity consists of seven rods to drop different wavelengths from eight cavities, each of eight drop waveguides. The design is very simple for realistic systems. The Finite Difference Time Domain (FDTD) and Plane Wave Expansion Method (PWE) methods are used to determine the proposed design's band structure and transmission spectrum. The resonant wavelengths are 1.5441μm, 1.5443μm 1.54449μm 1.5447μm 1.5449μm 1.5551μm 1.5553μm, and 1.5555μm respectively. The proposed device provides a high-quality factor, transmission efficiency, and low Crosstalk. The device's footprint is 451.2 μm2 easily incorporated into a Photonic Integrated Circuits (PIC).