In order to solve the problem of detecting and tracking small infrared targets under the complex sea-sky background, a detection and tracking algorithm for the small infrared targets under the complex sea-sky background is proposed in this paper. In the detection stage, in order to suppress all kinds of clutter in different regions, the algorithm uses different classifiers to distinguish the clutter and small targets in different regions. In the tracking phase, in order to further eliminate isolated noise and clutter interference, the Gaussian mixture probability hypothesis density filter is adopted to track the target. Detecting and tracking experiments on the simulation video show that the proposed algorithm performances better than the previous algorithms, that improves the correct tracking rate about 10%, and the tracking precision about 50% on average. The algorithm has good engineering feasibility.