Abstract: Star centroid extraction is an important basis of star sensor. As for the complicated noise condition of offshore star image, a new star extraction method based on gravity method was proposed, which included four steps: block scan threshold segmentation, noise rejection based on star continuity, star extraction considering gray information and gravity method for centroid coordinate calculation. The algorithm was proved in experiments using 30 offshore star images that it could extract at least 10 stars centroids correctly with a success rate of 100% and an accuracy of 1/20 pixel while achieving real-time processing for video. Application requirements of shipboard star sensor could be satisfied.