Aiming at detection puzzle of small target in grayscale image with low SNR,the characteristics of infrared small targets were analyzed and a detection algorithm was put forward based on multistructural element morphological filter combined with adaptive threshold segmentation.In view of the continuity and regularity of motion for target and the randomness of generation for noise,and considering the characteristics of structure element,the design of morphological filter and a technique via assembly line and pipe scheme were considered to detect target trajectory.Experiments show that the algorithm is able to obtain excellent results toward low SNR infrared image under complex background,and has high detection probability,high speed and low false alarm rate.