Developing automatic shallow water bottom topography detection algorithm is a key technique for coastal ocean monitoring. A new method was proposed to retrieve the orientation of shallow water bottom topography from SAR imagery, and the result was in accordance with SAR image characteristic. The feasibility and adaptability of using invariant moments to descript region of shallow water bottom topography were studied. We proved that this method can be used to detect a region with or without shallow water bottom topography. Finally, we proposed a shallow water bottom topography detection algorithm for SAR images based on average invariant moments and redefined distance of invariant moments with reasonable accuracy.