High resolution radar accumulated target echo on multiple range cells to improve the detection performance of range-extended target. When the target scatterers are sparsely distributed, the conventional algorithm of energy accumulation and detection has the subsided loss. The detectors based on scatterers can make up the problem of performance degradation caused by the collapsing loss. In this paper, the otsu algorithm was adopted to adaptively obtain the information of target scatterers. The result of simulation experiment showed the efficiency of the method.