The water sample has been collected from South China Sea. It is consistentwith the mean ocean water in the contents of major ions as well as H and O isotopes. The isothermal evaporation of the sea water has ben carried out in laboratory, where the evaporadon temperature is strictly controlled at 25℃. During theevaporation, the solid phases of salts separate frem water in the same sequence astEe former researchers reported.The H and O isotope ratios have been determined on both the changing residual water and the crystallization water within the deposited salts (including Gy, EPand Car) in the course of evaporation. The H and O isotope fractionation duringisothermal eyaporation of sea water has been displayed well in the distribution pattern of the isotope data. The enrichment of heavier isotopes continues to the latestage of Halite crystallization. Then, the δ13O and δD reach their highest valuesof 35‰ and 130‰ respectively. When Ep separates, the H and O isotope ratiosbegin dropping and dropping. On the other hind, the H and O isotope ratios ofthe crystallization water within the deposited salts increase from Gy, Ep to Carwhile the evaporation goes on. In addition, pH, Eh and specific weight valueskaye been gauged for the changing residual water during the evaporation, whichhave been contrast with the isotope data.The above result is up-to-date. It could provide a basis to further discussionabout the formation of brine and the process of marine salt deposits.