Liquid crystal polarization grating is a new type of grating device based on the principle of geometric phase. It can modulate the phase and polarization state of incident light by adjusting the spatial distribution of the optical axis of liquid crystal. Traditional liquid crystal polarization gratings can achieve high diffraction efficiency at normal incidence and a small spectral bandwidth, but it is difficult to maintain a high diffraction efficiency with broad spectral bandwidth, and the diffraction efficiency decreases significantly when incident at a large angle. The proposed multi-layer twisted structure allows these problems to be solved, but introduces a new problem, how to accurately control the twist angle and thickness. Based on this problem, this paper proposes a new method for measuring the twist angle and thickness of a liquid crystal polarization grating based on Jones matrix. The difference fitting method eliminates the error caused by the refractive index change of the entire waveband, and can accurately obtain the twist angle and thickness of the liquid crystal cell. The similarities and differences between the twisted liquid crystal film and the twisted liquid crystal polarization grating are analyzed. Based on the measurement results of the twisted liquid crystal film, the twist angle and thickness of the liquid crystal polarization grating prepared under the same conditions can be obtained. The experimental results show that the thickness measurement error is less than 2%, and the twist angle measurement error is less than ±0.5°. This method can quickly and conveniently realize the accurate measurement of twist angle and thickness, with high measurement accuracy and stability. The relationship between the concentration of the chiral agent and the twist angle is analyzed, which provides a theoretical basis for the preparation method of multi-twist liquid crystal polarization grating.