Abstract: A comprehensive method of identifying abnormal behavior of ships concerning both ship's navigation status and position is introduced. The navigation status is sorted into 3 categories, go straight, turning and staying, and the right distribution of ship's navigation status over the grid cells of the water area. The position feature of ships is extracted with kernel density estimation method and the normal position distribution of ships over the grid is found. These two distributions form the reference to find abnormal behavior of ships. The method is verified in the water area of Caofeidian. The method is proved effective in finding ship's abrupt change of course or/and peed, given the threshold has been appropriately set.