Abstract: To detect the weak target in the heavy sea clutter, after the intrinsic mode functions (IMFs) of the sea clutter and the inuence of the target on them is analyzed, it is found that the energy of the pure sea clutter is focused on the former 3 high frequency IMFs, but the proportion of the latter low frequency IMFs energy to the whole sea clutter energy becomes larger since it is affected by the appearing target, on the base of which, the proportion of the low frequency IMFs energy is proposed to detect the weak target. Compared with the weak target detection method directly using the box dimension or the multi-purses Cell Average CA-CFAR(100 pulses) method, it’s better to detect the slowly uctuant target in the sea clutter by the method proposed in the paper.