The Chukchi Sea is one of the marginal seas in the Arctic Ocean, where the sea ice cover varies seasonally. Herald Shoal located in the middle of the Chukchi Sea is a main feature of topography, and obviously impacts the flow and sea ice melting process. Data collected during the first Arctic cruise of China in the summer of 1999 are used to identify the water masses of Chukchi Sea around the Herald Shoal. Two water masses exist in this region. One is the Anadyr Water that entered in winter or spring with lower temperature, higher salinity and higher silicate. The other is the Bering Shelf Water with higher temperature, lower salinity and lower silicate. In open water, the maximum temperature in upper level reached 7℃, higher than local air temperature, which is speculated to cause by heating of local solar radiation. The water from open area inset under the ice cover to form a warm water region under ice with the temperature greater than 1℃, which leads to ice melting. Obstructed by the Herald Shoal, the northward flow bypassed the shoal and formed a cold water region under ice behind the shoal with the temperature lower than -1℃. Although the thickness of mixed layer in open water is about 15~20 m, the thickness of the warm water under ice is only 5~6 m, showing retarding of ice cover to the inset water. At the depth of 10 m under ice cover, the concentration of chlorophyll was higher in all stations, indicating the blooming under ice and impacting possibly on the heat absorption of water and ice melting.