Abstract: The Qinlan port, including its adjacent sea,is a complex depositional system,which consists of the southern and northern bays connected by tidal path,and theshallow beaches on both sides of the tidal path.The analysis of their surfacesediments showes that the depositional features of the sediments are controlled by theenergy conditions and material sources. According to the sedimentological analysis, the authors recognize two kinds ofdepositional features from the environments mentioned above,(1),the NorthernBamen Bay and northern part of the tidal path represent one kind,in which the riverprocess plays the main role but the tidal process takes some influences, too.Mostof the sediments in this kind of environments are terrigenous debris with smallamount of intrabasin organic fragments. The sorting is poor or very poor and thesize ranges from coarse to fine; (2),The southern part of the tidal path and Gaol-ong Bay connecting with off-sea represent another kind of environments in whichthe tidal process plays the main role but the river process takes some influences.Its main sediments are intrabasin fine一size organic fragments,sorting well,withquantities of terrigenous debris. Various sedimentological data of quantitativeanalysis indicate that the depositional conditions in the shallow beaches on bothsides of tidal path and the beaches with obvious erosion are in the medium statebetween the two kinds mentioned above. Waxing and waning of the river process and tidal process in the two sedimentaryenvironments which have different depositional conditions cause the debris to mix indifferent proportion and form the dynamic equilibrium of deposit supply and energyconditions,namely the dynamic equilibrium among transporting depositing andreforming of sediments. And this may be one of the important reasons that the adjacentsea of the Qinlan port and the tidal path may not accumulate in large amount ofterrigenous debris.