Abstract-Polarization properties of horn antenna are studied in the paper. The linear and circular polarized horns are simulated. There are four lobes in the cross-polarization pattern of linear polarized horn. And the phase of cross-polarization is changed at each bound of the quadrants. That of co-polarization, meanwhile, keeps almost the same value. There is a notch in the center of circular polarized horn cross polarization pattern. And the phase of both co-polarization and cross-polarization is continuous. Far field and near field measurement of horn antenna is analyzed to demonstrate the simulation.