The working principle and basic structures of IR GaAs liquid crystal light valve are described and the one-dimensional equivalent circuit model for IR GaAs liquid crystal light valve is constructed. According to above model, the influence of thickness of photo semiconductor layer-GaAs on the dynamic modulating range and driving frequency and resolution of IR liquid crystal light valve has been analyzed. The relevant curves and the optimal thickness range of GaAs have been given. The structure parameters of liquid crystal light valve are calculated accordingly and the liquid crystal light valve is redesigned and a part of experimental results is given.