Optical measurement is a very important science in present times. Generally, optical interference is applied in precise measuring. In this thesis, we use the opto-electric properties of liquid-crystal layers and the phase-shifting shearing interferometer will be applied. Clear patterns should be figured when measuring optical properties traditional interferometers. A new interferometer called phase-shifting shearing interferometer was developed recently. It is not necessary to appear clear patterns in measurements. In application to this interferometer, the phase information got by way of shifting the reference lens that can control phase differences. Phase controlled in thus method is mostly by the step motor or the PZT installation. Now we replace this installation by liquid-crystal layers since the accuracy of liquid-crystal layers controlled by voltage is better than the mechanical installation. The measuring precision is improved wide. In this paper, we study the optical properties under the application both DC and AC voltage to a series of thickness of the liquid-crystal layer, and the suitable condition of liquid-crystal layers to apply to the phase-shifting shearing interferometer.