In view of limitation in correlation detection algorithm of weak and small infrared target,the combined correlation detection algorithm is proposed,which synthesizes the merits of correlation detection algorithm based on the Detect-before-track(DBT) and correlation detection algorithm based on the Track-before-detect(TBD) as two algorithm cascade method.First,the correlation detection algorithm based on TBD is used to form a transition frame,and then the correlation detection algorithm based on DBT is used to further detect.In certain detection time,the algorithm can make full use of target space and time information to further enhance target detection ability in the small and weak target infrared sequence with low signal-to-noise ratio.Algorithm performance analysis and experiment results prove that the validity of the algorithm in the condition of low signal-to-noise ratio.