The bay is a sea surrounded by three sides, the other side is the sea, with U-shaped and circular arcs, etc., usually the connecting line between two corresponding capes near the bay mouth is the outermost boundary line of the bay. The opposite of the bay is the sea otter that is surrounded by the sea on three sides. The area occupied by the bay is generally larger than that of the fjord. 1 Due to the different degrees of softness and hardness of the rocky coast extending to the ocean, the weak rock layer is continuously eroded and recessed into the land, gradually forming a bay; the hard part protrudes into the sea to form a horn. 2 When the sediments in the longitudinal movement of the coastal sediment form a sand mouth, the side of the coastal zone is blocked and the concave sea area is formed. 3 When the sea surface rises, the seawater enters the land, the shoreline becomes zigzag, and the recessed part becomes the bay. Due to the occlusion of the shoreline on both sides, the bay forms a wave shadow zone in the bay, which reduces the energy of waves and tides. Sediments deposit on the top of the bay to form a beach. When the energy of the transported sediment is insufficient, the barrier dam can be formed in the bay mouth and the bay, which are called Wankou Dam and Wanzhong Dam.