Abstract: The full description of the formation, development and disappear of Qiantangjiangtide by numerical method is presented in this paper in details. In Hangzhou Gulf(near Ganpu),the water region is very wide and the water wave movement are two dimensional, then the two dimensional Saint--Venant equations are used to discribe the movement of waterwave from HangzhouGulf to estuary of Qiantangjiang River (Yanguan). In the Qiantangjiang River (before Yanguan),the water region is narrow and the river is very long, t...