Using salinity database of World Ocean Atlas 2009 (WOA09) issued by NOAA in 2010, refer the range of high-salinity tongue to indicate the strength about high-salinity water, from the perspective of structural changes of salinity; the water exchange through Ryukyu Islands upper 500 m have been analyzed, the results show that: due to Ryukyu Trough, currents on both sides of Ryukyu Islands occur exchange, for upper 500 m, high-salinity water in east of the Ryukyu Islands mainly invade the west waterthe Kuroshio in East China Sea; the intrusion strength is powerful from the depth of 100 m to 200 m, and the 150 m layer is the core layer of high-salinity water intrusion; the high-salinity water at the east of Ryukyu Islands invades the Kuroshio are stronger in March, May, June, September, October and November, are weaker in April and December.