To the complex background suppression problem in infrared small target detection over long distance, a method combining spatial filtering with wavelet filtering was presented.By using the gray-scale morphologic top-hat transform of adaptive structure element in the spatial domain, most infrared background was suppressed.On this basis, the processing space was transformed to the wavelet domain.By analyzing the difference of residual background, target and noise coefficients in high-frequency sub-band, the expression of sub-band coefficient based on neighbor average was defined, a center vector of high-frequency sub-band coefficient was constructed, and the wavelet high-frequency image was integrated to form a distance image, obtaining the final suppression result of infrared complex background.The experimental results show that: Compared with the classic algorithm, the method given here can not only effectively suppress the infrared complex background, but also strengthen the target signal intensity.