With development of regional economy and population,Modaomen Channel in the Pearl River Delta has become an important water source field for the cities of Jiangmen,Zhongshan,Zhuhai and Macao.Based on the observed data and field survey,this paper researched the change of tidal saltwater,response mode of runoff and salty tide,influence of wind,trend of historic development and variations,minimum discharge for overcoming saltwater intrusion and best opportunity.The results show that runoff is the main effect on tidal saltwater intrusion with the north or northeast wind.According to calculation,the minimum discharge for overcoming saltwater intrusion should be 2 200-2 700 m3/s in Modaomen Channel,the average discharge should be 2 450 m3/s,and the best opportunity is within the ebbing tide duration in syzygy period.