A background suppression method based on multi-scale Hidden Markov Mode (HMT) was proposed to remove the complex background clutter in the detection of dim and small targets. According to difference of distributed characteristics between target and background clutter in infrared image, the shearlet transform based multi-scale HMT was estimated by using the different scale and direction relation of inter-scale and cross-subband coefficients of decomposed images. Finally, the expectation-maximization(EM) algorithm was used to calculate the background, separate dim and small targets and background clutter of infrared image and to implement the suppression of background, and the preservation and enhancement of target signals. Compared with Max Median (MMed) and Local Means Remove (LMR) filter from subject inspection and value index, several groups of experimental results demonstrate that the proposed method can suppress the complicated background in dim and small target images effectively(SCR>=1.6).