In order to solve the problem of infrared dim and small target detection under the complex background of infrared, a detection algorithm for dim and small targets in complex background based on background adaptive multi feature fusion was proposed. Firstly, the isolated noise points are removed by spatial filtering of infrared images, and the constant false alarm rate was used to eliminate large area stationary background and obtain a suspected target set. And then most of the false targets in the suspected target were eliminated by combining the background information of the infrared image, the gray feature of the dim and small moving target and the direction gradient feature of the target and the surrounding pixels. Finally, the detection of infrared dim and small targets in complex background was realized. The experiment shows that the algorithm can realize fast infrared dim and small target detection with low signal to noise ratio under complex background, which has the characteristics of high detection probability, fast speed and good robustness.