The paper analyses the salinity distribution and salt-fresh water mixing of Yangtze River estuary by the recent three months hydrology data .The lamination factor and the mixing ratio concept are applied to analyse the mixed type.The result shows that:The salinity of the North Branch is the highest of the four sub-channels and changes greatly between floods and droughts .The North Branch is a typical well-mixed estuary the whole year.The salinity of the three south branches ranks from high to low as follows:the South Passage,the North Passage and the North Channel.The fresh and salt water mixing intensity ranks from high to low as follows:the South Passage,the North Passage and the North Channel,which is adapted to the situation:the water discharge of the North Channel is the highest,secondly the North Passage,the South Passage is the lowest.The mixing intensity of dry season is higher than flood season,while the mixing intensity of spring tide is higher than neap tide.The mixing intensity display cyclic variations over time,which is the highest around the maximum flood and the intensity of flood tide is higher than ebb tide.