Abstract: Sediments were sampled on the muddy tidal flat at the estuary of the Shuangtaizi River, and studied were the distribution pattern of trace elements, element assemblages and correlation of individual elements in order to seek for the mechanisms of transportation and enrichment of the trace elements and their dominating factors. The results show that all the factors, such as fresh water input, seawater properties and human activities are all effective on the spatial distribution of trace elements. Cu, Pb and Zn are rich in muddy deposits, but V is relatively poor. Apart from Ti, Ba, Sr, Zr, concentrations of other 11 kind of elements are higher in the high muddy tidal flat but lower in the middle and low tidal flats. Three assemblages of trace elements were identified by R-factor analysis, including the assemblage of siderophile and chalcophile elements represented by Mn, Rb, Co, Cu, the assemblage of potasium minerals related elements represented by Sr, Ba; and assemblage of clay related elements represented by Nb and Y.