Abstract: The CTD data collected from 17 stations in the central and eastern part of the South China Sea on May 7, to 25, and July 1 to August 23 in 2012 indicate that under the influence of the South China Sea warm pool, the sea surface temperature at the study area was higher than 28℃. It decreases from north to south, and from west to east, whereas the surface salinity was about 32psu/m or higher, and decreases from south to north and from east to west. The low salinity occurs in the northwest area, coincident with the high-temperature region. Water stratification is strong due to the impact of the summer monsoon and the net surface heat flux. The mixed layer is thin in thickness. The thermocline is well developed and may be up to 170m in thickness, and the gradient is higher than 0.09℃/m. The depth and thickness of the upper boundary of the halocline are lower than the thermocline. Combined with the distribution of surface temperature and salinity in the eastern and southern area, it suggests that there occurs a thick layer of water with low temperature and high salinity.