In view of the rapid increase of siltation in navigation channel in Nantong waterway,we analyze the intrinsic and external factors of siltation by the combination of measured data and mathematical model.The results show that,the dynamic is dispersed and weakened as the width of Nantong waterway widening from 2 km to 6 km,then sediment deposite and shoal underwater is formed,and the shoal underwater is transported crossing the navigation channel under the influence of circulation flow.The Hutong Yangtze River Bridge and the Tongzhou shoal west channel regulation are the direct causes of the rapid increase of siltation in navigation channel.The abundant sediment scour from Fujiang shoal waterway provides part source of siltation in navigation channel.