Abstract: Estuary sand islands are often developed in the estuaries of large rivers due to massive sediment accumulation and tidal action. Chongming Island is a typical estuary sand island in the world. In recent years, with the sharp decrease of sediment discharging in the Yangtze River Basin and the construction of many large-scale water conservancy projects, the sedimentary environment around Chongming Island have been profoundly affected. Based on the sampling data of surfaced sediment of 14 beaches’ cross sections between September 2015 and April 2018, we analyzed the characteristics of the tidal flat sedimentary environment around Chongming Island and its differences between regions and discussed the processes of sedimentation and mechanisms of different tidal flat sections. The results are shown as follow: The tidal flat sediment around Chongming Island is dominated by sandy silt and silty sand. The average of the median size of sediment is 48 μm, which displayed that the size sediments in south coast are largest while those in east coast are the smallest, and the sediment in north coast is between the above. In general, the south and north coasts have steep slope and narrow beach, and the slope of tidal flat on the north coast is slower than that of the south coast whose sediments become finer from west to east. The slope of the north coast is slow, and the area in the south coast between Chongtou and Miaozhen exists fine sediment. However, the east coast has slow slopes and wide beaches whose sediments become finer from the south to north. On the tidal flat profile, the content of clay components at high tidal flat is relatively high, and the sediments become finer with the water depth decreases. The river regime evolution of the Yangtze Estuary forms the sedimentary environment of the tidal flat in the north and south coasts of Chongming Island. It is obvious to influence the distribution of sediments because of runoff and tidal current. The wind wave has a strong sorting effect on the sediments of the Eastern Chongming Island. Tidal vegetation mainly affects the distribution of fine sediments in the intertidal zone. The decrease of sediment discharging has a significant impact on the sedimentary environment in the Eastern Chongming Island.