Based on liquid crystal, a wavelength tunable guide mode resonance filter (WTGMF) with a center wavelength of 1.55 μm is designed and optimized by using the rigorous coupled wave method. From calculation, the thicknesses of anti-reflection layer and substrate both have influence on the resonance line width of the filter. The thinner the thickness of anti-reflection layer is, the wider the resonance line width is. However, there is always an optimum substrate thickness to minimize the line width. When the substrate thickness is 300 nm, the resonance width is the narrowest with only 0.96 nm. In addition, the main factor that determine the wavelength tuning range of WTGMF is the thickness of the liquid crystal layer. The tuning range increases with the increase of the thickness of the liquid crystal layer and finally reaches stability. When the thickness of the liquid crystal layer reaches 1600 nm, the wavelength tuning range reaches the maximum of 39 nm.