Complex background suppression of infrared dim and small target detection is a key problem for finding long-distance target in infrared warning system. A complex background suppression algorithm based on multiscale truncation, which combines the singular value decomposition with the dual tree complex wavelet transform (DTCWT), is presented. Firstly, DTCWT is adopted to decompose the input infrared image, which extracts multi-scale detail features of images. Then, according to difference between targets and background clutter signals, the singular value decomposition is introduced to process sub-bands, and maximum eigenvalues are utilized to compose the sub-bands. Finally, the image is synthesized by the modified sub-bands, then targets and background details are separated, by which background suppression is realized. Experimental results validate that the presented method could suppress the structured background in some degree, and preserve and enhance the target signal.