It is important for the infrared thermal imaging system to increase the detection probability of small targets by resisting the interference of similar targets such as clouds, fog and objects on the ground. In order to decrease the false alarm rate of infrared surveillance system, a method for resisting of similar targets is put forward based on single infrared image. Firstly, the background noise is removed to enhance the SNR of infrared image. And then, according to head, tail and the length characters of targets, some potential targets are separated from the similar targets. The experiment result shows that this algorithm can decrease interference of similar targets and increase detection probability of infrared small target, and is very useful for small target detection.