The novel parallel-aligned liquid crystal spatial light modulator(LC SLM)is introduced,which is designed to operate at phase-only mode for wavefront correction. The optical characteristics characteristics of the LC SLM were measured and analyzed theoretically. The PV(Peak Valley)value of 0.07049λ(λ=0.6328 μm)after correction on the area of 1 cm² was obtained with our phase-only LC SLM.And Strehl ratio of 0.989 in our experiment indicates the approximate upper limit of the ability of LC SLM to correct a aberrated wavefront when it is used in adaptive optical system.