Abstract: In this paper, the production mechanism and the Doppler spread of the first sea-clutter in the Hybrid Sky-Surface Wave Propagation Mode are investigated. Then, the Doppler shift and spectrum spread formula are induced. Combined with coordinate conversion formula, the distribution and spread characteristic of the first order sea-clutter along range and azimuth are calculated and discussed. By compared the feature of the sea-clutter trial spectral with the theoretic distribution and spread characteristic, the experimental results accord with theoretic, which testifies that the conception of hybrid HF sky-surface wave is tenable. Simultaneously, the technical feasibility of this radar system is also tested.