Abstract: More and more countries pay great attention to HF(high frequency) ground wave OTHR (over the horizon radar) for its military and civil foregrounds. As to HFOTHR which works at shortwave band, useful targets should be detected from strong sea clutter. When sea state is well developed, the second order sea clutter becomes the main detective background. Based on analyses for mechanism of the second order sea clutter in HF radar, this paper discusses a method for emulating the second order sea clutter. According to the mechanism of sea diffraction the second order sea clutter is emulated, and the method is proved effective by contrasting with real spectrum of sea clutter.