Abstract: In the application of ultra-wideband antenna phase interferometer system, it is found that the system is sensitive to the polarization characteristic of the antenna, which seriously affects the angle measurement accuracy, especially in the low frequency band. The polarization characteristic of an ultra-wideband antenna were modeled, and the influence of polarization characteristic of the antenna on the polarization characteristic of incoming wave is analyzed, which finally leads to the decrease of the angle measurement system of the phase interferometer. The influence of polarization characteristic of the ultra-wideband antenna on the angle measurement accuracy of the phase interferometer is verified by practical test, and a way to improve the angle measurement accuracy is proposed and the result shows that the way could improve the angle measurement accuracy obviously.