Liquid crystal polarization grating (LCPG) can achieve non-mechanical beam steering. During the actual preparation of LCPGs, the filling of liquid crystal molecules is not uniform, resulting in uneven liquid crystal layer thickness, which reduces the diffraction efficiency of light through the same position of the effective region of cascaded LCPG. This study analyzes the influence of driving voltage on the diffraction efficiency of LCPG based on Jones matrix theory to improve the diffraction efficiency of cascaded LCPGs. An experimental device is constructed for beam deflection using a three-stage cascaded LCPGs. The spot energy is measured by applying varying driving voltages, and the relationship between the diffraction efficiency and the voltage is obtained. The experimental results show that the +1st-order diffraction efficiency reaches 0.80-0.84 when the voltage is in the range of 2.0-2.4 V.