The infrared small targets in complex background are not easy to detect due to their fuzzy edges, and the false alarm rate is high.To solve the problems, an improved Top-Hat target detection method based on SUSAN background suppression is proposed.In this method, the background of the original image is suppressed by using SUSAN method, and then an opening operation is made to the suppressed image.Finally, the result of the opening operation is compared with the original image, and the result images are obtained by assigning values to them respectively.In order to verify the superiority of the improved Top-Hat method, the image after background suppression is processed respectively by using the traditional Top-Hat method and the improved Top-Hat method.The comparison results show that, the proposed algorithm can greatly improve the detection probability of infrared small targets in complex background, and effectively reduce the number of false targets, i.e., the false alarm rate.