At present, the deflection angle of orthogonal cascaded liquid crystal polarization grating is considered to be an integral multiple of its angular resolution. Actually , there is deviation between the actual deflection angle and the design angle of the orthogonal cascade liquid crystal polarization gratings. To solve this problem, the deflection angle formula of cascaded liquid crystal polarization gratings is derived according to the angle deflection theory of single-chip liquid crystal polarization gratings firstly, and then the deflection angle model of two-dimensional orthogonal cascaded liquid crystal polarization gratings is derived, the relationship between the deflection range and the angle resolution of two-dimensional orthogonal cascaded liquid crystal polarization gratings is analyzed, and the actual angle resolution satisfying a certain angle range, the angle range that satisfying the actual angle interval and the design angle interval that satisfying the angle range and angle interval at the same time is calculated respectively. Finally, A software model which measurement accuracy is 0.1° is established use optical design software and a construction which measurement accuracy is 0.1° are established,they prove that the angular deflection model is accurate.