In order to solve the problems of high detection error rate and long detection time in the detection process of complex background infrared dim dim targets, a detection method of complex background infrared dim dim targets based on full convolutional network is proposed. This paper analyzes the research progress of complex background infrared dim small targets detection, finds out the defects of different methods, collects infrared images, extracts target detection features, and uses the full convolutional network to design a classifier for dim small targets detection, and realizes the detection of complex background infrared dim small targets. The experimental results show that the accuracy of this method is more than 97%, and it has high practical application value.