Photorefractive waveguide grating can be formed using two-beam interference method in lithium niobate with the single-mode waveguide. A scheme for Coarse Wavelength Division Multiplexing (CWDM) is proposed to realize tunable filter by changing the angle between the two recording beams which changes the grating pitch. With photorefractive dynamics, tuning time of several milliseconds is obtained. It is found that diffraction efficiency can be increased and the building time decreased by suitable intensity and dopant. The results based on coupled wave theory show that diffraction efficiency can be increased and bandwidths narrowed when the grating length is increased, and diffraction efficiency can be increased but bandwidths widened with the increasing refractive index modulation. When refractive index modulation is 8×10-5 and the grating length is longer than 12 mm, diffraction efficiency more than 91% and bandwidth narrower than 0.08nm can be obtained.