Photonic crystal coupling waveguide is developed when line defects are introduced into photonic crystals. The finite-difference time-domain (FDTD) method is applied for analyzing the waveguide coupling of 2-D square lattice photonic crystals. Transmitivity at exits of photonic crystal waveguide with different coupling length is given. Results indicate that photonic crystal waveguide coupling follows general regulation of conventional dielectric waveguide coupling. Further studies show that coupling coefficient of the photonic crystal waveguide directional coupler is different, coupling coefficient is linear with the corresponding frequency.