Based on the principal theory of tripole antenna in free space to compute the polar angle and azimuth angle of the incident electromagnetic wave (EMW), and the relations between each component of electric field and polarization, the formula for computing direction of arrival (DOA) of left-hand polarization electromagnetic wave and the method of determining the sense of the incident wave are presented. A novel method to filter out the reflected wave from the earth surface is put forward, which ensures the accuracy of the DOA, various polarization parameters are gained from DOA computed and electric field intensity, these polarization parameters serve as reference data for research of ionosphere and electromagnetic wave propagation in the ionosphere.