Small target is also weak target, which is likely to be a threat to the observation platform. So small target detection is an important task for many automatic object detection system. Otherwise, small target detection is a challenge for many complex scenes because of the low SNR and sophisticated background. This paper introduced a fast and effective method for small target detection in infrared scene with complex background, which is suitable for missile guidance and menace warning. Firstly, a template is created to detect the local maxima in the image. Secondly, a constrained double criteria region growth algorithm is performed to form separate regions. Finally, extracted regions are selected by a small round target filter, after which, the remaining connected regions are considered to be detected small targets. The proposed algorithm was applied on videos captured by cooled infrared imagers. Experimental results show the method introduced in this paper is efficient and effective, which is suitable for time sensitive automatic target detection.