Without detection of the location of sea-sky line in advance,a feasible method combining with the characters of marine visible images and a complex sea-sky background was proposed to detect distant weak targets in the sequential images from a surface vehicle. Firstly, the images damaged by the noise such as exposures and reflections was mended by the border color of ruined range. Then, the complexity of sub-images and their neighborhood average gray difference were measured to predict the sea-sky region.If the sea-sky region was obtained,the location of the sea-sky should be predicted. Otherwise,the consequent process of images could be eliminated. The strategy of filtering and clustering in Mean-shift segmentation was adopted,in which the surround suppression filter was applied to smoothing the sea-sky region and the smoothed image was clustered by taking the pixels and points as units. Finally, the largest region was assumed to be the background and the rest was taken as target information. The experiment results prove that this method can locate the objects efficiently and the time cost is 35 ms/frame, which is robust and real-time.