[Objective] The water sources of alfalfa and seabuckthorn under different vegetation allocation patterns in drought and rainy seasons were studied to provide a theoretical basis for vegetation restoration in mining areas. [Methods] The platform of the dumping site of Manlailiang coal mine in Ordos City, Inner Monglia Autonomous Region was taken as the research area. The stable isotope technique was used to collect plant xylem samples, soil samples, and precipitation samples under three vegetation configuration modes in the study area, and the hydrogen and oxygen stable isotope compositions were analyzed. [Results] ① With the advent of the rainy season, the soil moisture content of all plots showed an increasing trend. The pure seabuckthorn land increased from 6.56% in the dry season to 9.88%, the pure alfalfa land increased from 7.94% to 9.15%, and the mixed land increased from 9.4% to 15.45%. ② Alfalfa and seabuckthorn mainly used 80—100 cm soil water as their water source under different vegetation configuration modes in the dry season. In the rainy season, with the supplement of rainfall to soil water, the soil moisture content increased, and the water absorption depth of various types of vegetation moved up, mainly concentrated at 20—60 cm. [Conclusion] The water sources of alfalfa and seabuckthorn were very different in the dry and rainy seasons under different vegetation configuration modes. In the dry season it was mainly concentrated in deep soil, and the water absorption depth moved up and the water absorption range increased in the rainy season. To avoid resource competition, seabuckthorn will choose deep soil water as its main water source under the mixed condition in the rainy season.