Hydrogen and oxygen isotopic composition of soil water was an effective substitution index for water use pattern in soil-vegetation system.In this paper,we selected Ansai and Shenmu as study area and collected soil water in different ecological system after rainfall.The results indicated the hydrogen and oxygen isotope of soil water was mainly controlled by soil property and climatic conditions,and had a weak relation with the vegetation coverage.In Ansai region,the hydrogen and oxygen isotope value of soil water under maize and green bristlegrass coverage declined linearly with the increase of soil depth,and got the lowest value at 80-100 cm depth.