To obtain an easily made grating coupler with stable materials, a proposal to fabricate photorefractive long-period gratings coupler on Ti-diffused LiNbO3 waveguide is presented. Structural parameters of the coupler can be determined by using effective index method and coupled-mode theory, including grating period as 74.28 mm, separation distance of two waveguides as 8 mm and the minimum grating length for 100% coupling as 2.42 cm. The transmission spectrum is analysed and the 3-dB bandwidth can reach 5.20 nm. The simulation results also show that coupling efficiency is above 90% when tolerance of grating length and offset distance is 0.37 cm and 0.21 cm, respectively. The coupler is expected to be used in coarse wavelength division multiplexing system.