In this paper, a new design of demultiplexer based on two-dimensional photonic crystal ring resonator is proposed. The structure is made of a hexagonal lattice of silicon rods with the refractive index 3.46 in coefficient of air with refractive index 1. The transmission efficiency and Quality factor for our proposed demultiplexer, respectively, are more than 65% and 1600. The normalized transmission spectra of the photonic crystal ring resonator are taken using Two-dimensional (2D) Finite Difference Time Domain (FDTD) method. The photonic band gap is calculated by Plane Wave Expansion (PWE) method.