The spatial polarization characteristic of radar antenna is modeled in this paper. And based on it, a novel polarization estimation method of incoming wave signal is proposed. It is indicated that co-polarized component and cross-polarized component of antenna satisfy even-odd symmetry property, respectively. This conclusion is confirmed by electromagnetic computation and real test data. Our method does not need auxiliary orthogonal polarized antenna. The polarization can be estimated by using only received signal power. The accuracy of measurement method is guaranteed and the realization complexity is reduced. Simulation experiment proved the availability of the method.