Abstract: The soil water regime in Populus euphratica forest was studied in the alluvial plain of Tarim River, Yingbaza section. Patterns varied according to the age of the forest stand: in young forest zones groundwater was 1-2 m deep and lightly salt (1-3 g·L-1). The zone is often flooded during typical high water stages and has a high content of soil water, it is suitable for the growth of Popular euphratica seedlings. In the mature forest zone, groundwater is 2.5-4 m deep but still slightly salt (1-3 g·L-1). As the zone is flooded only in especially wet years and the soil water content in the surface layer is low, the water condition significantly limits the growth of Populus euphratica seedlings. The depth of groundwater observed in these forests is in the reach of the roots of mature trees and the conditions are suitable for mature forest growth. In the degraded forest zone, groundwater depth was 5-10 m, exceeding the critical depth for typical growth of Populus euphratica and soil moisture supply is in seriously deficit, causing Populus euphratica stands to degrade and wither.