As a very important component of a coastal system,tidal flats come to be a focus of the studies on land-ocean interaction in the coastal zone because those areas are subjected to intense human activities and are highly sensitive to the global change.The Quanzhou Bay,located along the middle part of Fujian coast of China,covers about 136.4km2,and the area of coastal wetland in the entire bay from intertidal to subtidal with 6m of water depth accounts for 96% of the total area.Seven short cores were collected and divided in situ with the interval of 5cm on the coastal wetlands of Quanzhou Bay on April 19,2006.The sediment samples were scattered and the grain sizes were measured by using Mastersizer 2000.Human beings’ activities on tidal flat have disturbed the vertical distribution of sediments in stratigraphic sequence and accelerated the sedimentation rates.Grain size analysis results show that the grain size diameters increase and sediment becomes worse sorted towards the sea under the strong human disturbance;Spartina alterniflora can play a role of trapping the fine sediment;but near the bank,the sediment becomes coarse and there are two peak values on frequency curve influenced by the sandpile.The trough formed by human activities along the coastline changes the transport path of water and suspended sediment.The sediments are transported through the trough and deposit in it during the flood;the ebb flow is retarded by the flow output through the adjacent trough,and the deposited sediment can not be re-suspended;then,the sedimentation rate increases.In situ observation show that the sedimentation rate is about 8-10cm/yr. As a very important component of a coastal system, tidal flats come to be a focus of the studies on land-ocean interaction in the coastal zone for those areas are subjected to intense human activities and are highly sensitive to the global change.The Quanzhou Bay , located along the middle part of Fujian coast of China, covers about 136.4km2, and the area of ​​coastal wetland in the entire bay from intertidal to subtidal with 6m of water depth accounts for 96% of the total area .Seven short cores were collected and divided in situ with the interval of 5 cm on the coastal wetlands of Quanzhou Bay on April 19, 2006. The sediment samples were scattered and the grain sizes were measured by using Mastersizer 2000. Human beings’ activities on tidal flat have disturbed the vertical distribution of sediments in stratigraphic sequence and accelerated the sedimentation rates. Grain size analysis results show that the grain size than radial increase and sediment becomes worse sorted towards the sea under th e strong human disturbance; Spartina alterniflora can play a role of trapping the fine sediment; but near the bank, the sediment becomes coarse and there are two peak values ​​on frequency curve influenced by the sandpile. The trough formed by human activities along the coastline changes the transport path of water and suspended sediment are sediment through the trough and deposit in it during the flood; the ebb flow is retarded by the flow output through the adjacent trough, and the deposited sediment can not be re-suspended; then , the sedimentation rate increases. In situ observation show that the sedimentation rate is about 8-10 cm / yr.