The effective tracking for dim target in low SNR image sequences has become a hot research field in recent years. The characteristics of background, target and motion were deeply analyzed in this paper. A novel method was proposed to filter the background based on the continuity of the movement of small targets in image sequences. The SNR was enhanced considerably after filtering. The true dim target can be accurately tracked by using the feature of moving targets and motion information. The proposed algorithm astringes rapidly, and has a high accuracy. The experimental results show that the algorithm could detect and track small moving targets with efficiency.