The method of dim target detection based on spatio-morphological and wavelet transform clutter suppression is proposed. The image sequences are processed with spatial tophat filtering. The results are transformed into wavelet domain, and filtered by smooth filter in every wavelet belt, and the difference process is operated between the pre- and after filtering coefficients. The inverse wavelet transform is carried out to produce the residue image sequences with dim targets. The tophat filtered image is used to estimate the possible target support area. Under the restriction of the possible target area, the tempo-spatial data fusion is performed to detect the trajectories of dim targets. Simulation results show that the obtained residual images have very good white Gaussian normality, and the average gain of the target’s neighborhood Signal-to-clutter-noise Ratio (SCNR) can be improved obviously compared with traditional image smooth filtering and frequency filtering algorithms. The trajectories of dim targets can be detected steadily with 5 image frames.