Large tidal current ridges (tidal sand banks) in the southwestern Yellow Sea are located offshore of northern Jiangsu Province, China. These ridges radiate to a depth of 20-30 m. The dimensions of the ridge system are about 200 km long and 90 km wide. Their morphology indicates the strong influence of tidal currents. The ridges are composed of well-sorted fine sands (size range is 2-4 phi ). The grain size distributions of the sands show that the sands are transported and deposited by tidal currents. The ridge system formed on the abandoned Yellow River and ancient Yangtze River deltas has an abundant sand supply from the former deltas. Of particular importance is the existence of two tidal wave systems in the Yellow Sea: the rotary tidal wave system in the southern Yellow Sea and the Pacific progressive tidal wave system propagated into the southern ridge area of the southwestern Yellow Sea. Under the interaction of the two tidal wave systems, the huge tidal current system in the southwestern Yellow Sea has formed.