According to small moving infrared target detection in the sky background,a detection algorithm is presented through the characteristics of small moving infrared target,noise and background in infrared images are analyzed. Firstly,by utilizing the excellent quality of multi-wavelet,the infrared images is preprocessed with the proper pre-filter. Secondly,the coarse detection is performed based on differentiating tow neighboring frames in image sequence to extract candidate targets. Finally,the candidate targets are recognized by the characteristics of moving target and noise in order to detect real small moving infrared target based on. The effectiveness of the algorithm is proved by the experimental results for several real infrared image sequences.