Abstract: A method to measure the accuracy of phased array radar antenna after installation is discussed in this paper．According to the geometry modality of installation data of the radar antenna，the installation data of phased array radar antenna is collected with the optical instrument，the mathematic model of the examination is established，the data is matched with the linear regression algorithm and the least square algorithm，the maximum angle between the antenna undersurface and the horizontal plane and the angle between the antenna edge and the due north direction are calculated，the test error is evaluated and analyzed，the horizontal angle and the azimuth of phased array radar antenna are adjusted according to the detection data．The result shows that the accuracy of this method is better than that of the single measurement method and thus the pointing accuracy of the phased array radar system is improved．