Abstract: Compared with the single mode radar, because the transmitter and the receiver are separate, the first- order sea clutter of HF over the horizon hybrid mode radar based on sky wave transmitting and surface wave receiving presents different characteristic. This paper introduces simply elementary composing and operating principle of this hybrid mode radar system, considering the particular geometrical configuration of this system, derives its localization principle, combining electromagnetic wave propagating path and bistatic working mode of this hybrid mode radar, derives the theoretical calculation formula of the Doppler frequency of the first-order sea clutter, analyzes the phenomenon that the first-order sea clutter changes with different orientation, as well as verifies the theoretically analyzed result with practical metrical data.