Based upon a large amount of field data from the Wusong wakerworks and Gaoqiao Hydrographic Station,this paper analyses the characteristics of temporal and spatial variation of saltwater intrusion into the South Channel.Probabilities associated with different water qualities are calculated according to the probabilities of the corresponded fresh water discharges from the long records of the Datong Station.The water quality in the South Channel is affected by the saltwater intrusion each year,but the intensity varies greatly with different hydrologic years.