Photonic crystal is an artificial microstructure constructed in optical wavelength scale, whose dielectric constant arrangement is a periodic configuration. Because it possesses photonic bandgap, it can be used to control photons. Photonic crystal waveguide can be formed by introducing line defect. Given 1.55 μm TE polarized light as source and under different waveguide separations, the relationship between coupling length, coupling efficiency and refractive index of dielectric cylinders, radius of dielectric cylinders are calculated and analyzed by finitedifference time-domain method, respectively. These research results will provide a theoretical guidance for the structure design and fabricating of the 1.55 μm coupler.