Diffraction efficiency and scanning range determine the optical performance of liquid crystal optical phased array. To enhance the scanning range, it is necessary to fabricate high spatial resolution device. But due to the limitation of the nonlinear correlation effect, there is a tradeoff between the diffraction efficiency and the scanning range. The key parameters influencing the diffraction efficiency of optical phased array are elucidated based on the mechanism of nonlinear correlation. The effect of the material parameters and device structural parameters on the diffraction efficiency is also investigated, and suggestion is given to enhance the diffraction efficiency. Furthermore, to reduce the effect of nonlinear correlation, optimization method is employed to adapt the voltages applied on each electrode to enhance the diffraction efficiency and proved to be in effect, which will contribute to enlarge the scanning range of optical phased array.