Abstract: The target polarization characteristic is an important prior knowledge of signal algorithm of polarization radar seeker. It is of great significance to study the polarization characteristic of ground-sea clutter theoretically and experimentally for the development of polarization seeker. Statistical characteristics of ground-sea clutter in time-frequency domain and polarization domain are the basis of designing anti-jamming algorithm for radar seeker. Based on the Ku-band dual-polarized planar slot antenna developed by our laboratory, the frequency domain and polarization domain experiments of ground-sea clutter under vertical and horizontal polarization were carried out at a test site in Laizhou, Shandong Province, and a large number of experimental data of fully polarized echoes were obtained. The polarization of ground-sea clutter under given conditions was explored in terms of polarization degree, polarization invariant and polarization decomposition. The experimental data are processed and analyzed. In Ku band, the clutters in three typical environments basically have high polarization and obvious polarization characteristics. The polarization characteristics of the clutter are obviously changed with frequency transformation, which show the sensitivity of polarization to frequency. The polarization invariants of the three clutters are significantly different, and change significantly with frequency. The polarization decomposition results of the data verify the existence of the main scattering mechanism of the three clutters. The experimental results of ground-sea clutter provide an important basis for the design of polarization filtering and polarization recognition algorithm in radar seeker, and the test data also provide an application reference for engineering practice.