Aiming at the problem of the extraction for the target object in the complex images, the advantages and disadvantages of the common algorithm (background subtraction, optical flow and frames differences) in the pixel image processing and the applicable range are introduced. The method of the floating threshold in the small target image extraction and the algorithm design process are proposed. The experiment shows that the object can be quickly extracted by using this method, the image object after fuzzy classification is restored and the background is replaced by other color. The object extraction can be realized.