The small target detection method of infrared imagery in complex background of sea and sky in studied,and an algorithm based on wavelet analysis and mutual energy combination is presented.Wavelet Mutual Energy Combination (WMEC) functions are defined in horizontal and vertical directions. Targets are enhanced and disturbances of background are weakened efficiently by WMEC processing at the two directions. Targets are coarsely segmented with thresholds which are set automatically by a method of part gray histogram analysis. Results of coarse segmentation in the two directions are integrated, and targets are located by means of maximum energy judgment. The size of targets is decided by comparing the dissimilarity between a couple of windows. Experiment results indicate that the method can be appropriate in both kinds background of land and sea. It is with high correct detection ratio from a single image, and high speed to realize.