Abstract: The GNSS antenna phase center offsets affects the result of navigation positioning, so it can't be ignored for high-precision measurement. It is essential for GNSS antenna to measure the phase center offsets before high-precision satellite navigation surveying. With the analysis of antenna phase center offsets calibration process, a new observation model is established, which estimate the center of rotation and the phase center offsets by processing the baseline data based on least square criterion. This model does not constrain the rotation angel of the antenna and the number of the observed data, which improved the measure accuracy. The test results of GNSS-750 indicate that the proposed method can measure the antenna phase center offset with the measuring accuracy less than 0.05mm.