In order to realize the detection of i nfrared small target in complicated background,this paper proposes an infrared small target detection algorithm based on collaborative spa rse coding (CSC).The sub-image blocks are extracted from the testing image through sliding window from top and left to bottom and right,and then each sub-iamge block is transformed to a column vector,which is used as over-compl ete dictionary.The corresponding coefficients matrix and error matrix are calculated with the const ructed over-complete dictionary using the proposed collaborative coding model. Then,the coefficients matrix and error matrix are obtained using alternating di rectional method of multiplier (ADMM).And finally the location of the infrared small target is obtai ned through reconstructing the error matrix.Experiments are executed on both the synthetic and public data sets ,and comparisons with the state-of-the-art methods show that the proposed met hod is more effective and robust.