In this paper, a method called “superposition analysis” is applied to the study area, based on 8 MSS, TM satellite images from 1978~2004. Making use of a series of images, the authors studied the dynamic changes of mud flat and at the same time avoided the difficulty of tidal level rectification. Three approaches were employed to study the prograding dynamic changes of Songzhuang sea coast in Ganyu, namely, the alteration of seawall lines (mostly resulting from voluntary reclamation) built in past years, the expanding process of Spartina alterniflora and salt swamps, and the prograding rate of Linhong estuary. It is shown that this method can avoid the difficulty of tidal level rectification in different periods and reveal the dynamic change and prograding rate.