In order to measure the phase modulation characteristics of the liquid crystal optical phased array with 633 nm, the whose design wavelength is 1550 nm, the Tymann Green interferometry combined with the polarized light interference methods are used. The experimental results show that the phase delay of the liquid crystal optical phased array is a linear distribution. In 0~255 gray-scale range for 633 nm, the actual phase modulation is 0~3.76π. The phase modulation characteristics have a good linearity in 135~255 gray-scale range. It can be used as the liquid crystal work area. Since the accuracy and precision of the liquid crystal phase control are depend the loading gray scale to achieve, so measuring the relation between the phase delay and gray has an important value in high precision light beam deflection and tracking for liquid crystal optical phased array.