Abstract: In 1987～1995,precipitation,water from Black River,groundwater from Gurinai grassland and its vicinity were sampled positionally and periodically, groundwater and lake water from gobi and desert were sampled stochastically during the expedition into Badain Jaran Desert.Isotope composition of precipitation with its δD～δ¹⁸O fits the Craig Line while that of groundwater with anunusual deuterium excess of about -22‰ was found in this area.The formation of this isotopically anomal ous groundwater,however,is still not clear.The engineering impact of the planned Black River Project on groundwater is evaluated from comparing isotopic composition of waters.It seems unlikely that it would intensify the ongoing desertification of the Gurinai grassland area in the near future.But it seems to be important for the area by the Black River and,the Ejin Oases.