The arid area is one of the most concerned areas among the water resources researchers and economists. Northwest China will be an important developing region of China in the 21st century. Yaoba is a well-irrigation oasis within this arid area, which is located in the Alxa area west of the Helan Mountains and next to the Tengger desert in the east. It has contributed greatly to the local stock raising and agriculture since its development in 1970. However, the groundwater which the oasis depends on to survive has been getting salinized gradually and more serious in recent years.A comprehensive study was carried out using the methods of groundwater environment isotope analysis, lithofaci-es and palaeogeography, calculations of water-rock interaction and the existing form of chemical components in groundwater etc. It has been found that the salinization of groundwater is mainly caused by reinfiltration water solving the salt in soil which is deposited simultaneously with the sediments and accumulated in th The arid area is one of the most concerned areas among the water resources researchers and economists. Northwest China will be an important developing region of China in the 21st century. Yaoba is a well-irrigation oasis within this arid area, which is located in the the Alxa area west of the Helan Mountains and next to the Tengger desert in the east. It has contributed greatly to the local stock raising and agriculture since its development in 1970. However, the groundwater which the oasis depends on to survive has been getting salinized and more serious in recent years. A comprehensive study was carried out using the methods of groundwater environment isotope analysis, lithofaci-es and palaeogeography, calculations of water-rock interaction and the existing form of chemical components in groundwater etc. It has been found that that the salinization of groundwater is mainly caused by reinfiltration water solving the salt in soil which is deposited simultaneously with the sediments and accumulated in th