Abstract: Using the World Ocean Atlas 2005 for three-dimensional explorations and figure manifestation with Matlab computer program, internal structure of water temperature of the Kuroshio in the East China Sea (ECS) is researched, by analyzing the distribution and change of the 10% high temperature area (warm-core). The results show that, (1) from surface to 250 m depth, the distribution area of warm-core is moving from middle axes of ECS-Kuroshio current to the east border, and the warm-core range is reduc-ing from larger than 30~to about 10%. There is no distinct change in warm-core area below 250 m. (2) From the entrance to the exit of ECS-Kuroshio, the warm core temperature is decreasing with Kuroshio current from the surface to the depth of 200 m, but the temperature is increasing below the depth of 200 m. (3) There are two turn points of warm core of ECS-Kuroshio current; one is off the northeast of Taiwan Island, and the other is near 30°N where ECS-Kuroshio flows into Tokara Strait. The turn points are moving toward southeast with depth. The one off the northeast of Taiwan Island changes gradually in different seasons.