Flat structure factors are used in traditional morphology detection. In the process, infrared targets are regarded as isolated points without considering imaging characteristics of real, small and weak infrared targets. According to the problem, detection methods for infrared targets based on morphology with girdle structure are designed and traditional Top-Hat algorithm is improved. The improved algorithm is simulated by using real infrared target images. The results show that the algorithm has better suppression action in complex background comparing with traditional morphology methods.