A new segmentation algorithm, which utilizes boundary, area and texture features for segmenting extended target in complex environment, was proposed. the target was segmented preliminarily by series boundary technique based on knowledge, Then a new fractal segmentation algorithm was used to suppress the complex nature background blocks in the image. And the mathematical morphology method was utilized for eliminating the background conglutination. The experimental results indicated the validity of the method for segmenting the extended target in complex environment and that the method can reserve the shape details of the target perfectly.