Abstract: Aiming at the detection problem of HF fixed-frequency channel detection clutter background, a threshold extraction method based Rayleigh distribution map is proposed, and according to the multi-level threshold extraction result and the binary image mark and image expansion filling method based on run-length code, the background energy level profile of HF fixed frequency channel clutter is given, which provides support for subsequent detection research. The research shows that this method can give an ideal clutter background contour in the clutter in the clutter background segmentation of multiple HF fixed-frequency channel detection, which has a certain guiding effect on the subsequent sea clutter extraction and correlation detection.