For detecting moving dim spatial target in dynamic background space observation serial images,a method that combined image preprocessing and spatial filter based on target feature is proposed.The method include following steps.First,image preprocessing,it include background stars registration,background mask generation and background subtraction.Second,enhancing image by spatial filter based on target feature,detecting the maximum 8-connected regions,getting target′s coordinate through centroid method.At last,trajectory extraction through linear Hough transform and least square method.The effect of the detection method is verified by the result of experiments.