Abstract: In July,2011,the grain sizeand envionmental factors of surface sediments were surveyed in intertidal flat of Donghai Island,Zhanjiang.It was showed in the results that the samples can be clasified into fourtypes ingrain size:sand,silty sand,sandy silt and clayey silt.Sand and siltysand weretwo important types in the studied areas.The main sedimentary type was sand in three areas:Zhanjiang Bay(area I),Longhaitian area(areaⅡ)and Leizhou Bay(area Ⅲ).The silys and was the main type in Tongminghai area(area IV).The mean grain size of surface sediments was between 0.023mm and 0.342mm(1.55~5.46φ)with an average of0.092mm(3.45φ)at all sampling sites.As a whole,the grain size of intertidal sediments decreased gradually from high tidal region tolow tidal region,and creased slowly fom the west areas to the east along the south and north sides of Donghai Island.Most intertidal sediments were in a sorting statefrom the middle degree to the worse degree,and of skewed types from notable negative skewnes to positive skewness.Most pobability cumulative curves of grain size be-longed to flat-type and sharp-typepeaks.The sedimentary types and distribution characteristics of grain size embod-ied truly the dynamical differences of tidal curent in different intertidal areas of Donghai Island,and impacted di-rectly on the physical and chemical properties of sedimentary areas.Consequentlyin intertidal flatsof Donghai Is-land,the bigger the grain size,the higher pH and C₄/CF₂4,and the lower TOC and AVS contents.The envi-rommental factors above-mentioned showed that the contrary changed the rules when the grain size was smaller.