In military reconnaissance and aerial guidance by visible light, targets often conceal in a complex background and difficult to identify, so it is of vital importance to exactly extract feature utilizing image processing methods. Based on the characteristics of background and target, it is put forward that morphology can be used to determine target scope, and further combined with the method of clustering to accurately detect small objects. The experimental results show that the method can realize accurate recognition even in complex background and relatively smaller visual target area. The method can overcome the low speed of clustering and quickly and accurately extract the target with good adaptability.