Morphology filtering and order filtering are two methods used in image processing. First the image is pretreated by using the two methods,and then the target is distracted by using threshold division.The threshold is decided by the mean of the pretreated image gray and the variance. The image to be processed is star image under sky background. The result indicates that the target can be distracted from its noisy background in this way. At the same time,it also proves that while the target is larger than noise particles,using the two types of method can not only distract the target well,but also process fast.Moreover,the processing result of other image proves that the method is effecitve.