In order to determine the water use strategy of fruit-grass complex system in different habitats, we studied the hydrogen and oxygen isotopic values of soil water, xylem and stem water of single cropping apple (SA) treatment and fruit grass composite systems (apple+white clover (AW), apple+ryegrass (AR)) in Yangling of Guanzhong and Luochuan of Northern Shaanxi. Direct comparison method and IsoSource model were used to analyze the water use strategy of fruit-grass complex systems in different seasons under different habitats. The results showed that under different habitats, the vertical fluctuation of soil water content of orchard in Yangling area was larger than that in Luochuan area. The consumption of soil water in 40—80 cm layer in Yangling was greater than that in Luochuan. The planting of white clover in Yangling orchard in dry season would increase the consumption of deep soil water. In the dry season, the depth of soil water mainly used by apple trees was 40—100 cm (63.0%), and that of the forage was 0—20 cm (65.0%). The water use level of apple trees in Yangling was lower than that in Luochuan. The depth of soil water used by apple trees in SA and AW was 20—40 cm (54.3%), that in AR was 40-100 cm (65.0%). The depth of soil water used by white clover and ryegrass was 0—20 cm (59.3%) and 20—40 cm (62.2%), respectively. In the rainy season, the water source layer of apple trees in both places were the same, the depth of soil water used by apple tree in SA was 20—40 cm, that in AW and AR was 40—100 cm. And the forage intervention moved down the water absorption layer of apple trees. The results indicated that the fruit-grass complex system could adjust its water use strategy with the seasonal changes in different habitats. The fruit-grass complex system in Luochuan area responded more quickly to the water change, and increased the use of deep soil water when water was insufficient to avoid water competition. And it had a better adaptation mechanism to habitat heterogeneity than that in Yangling. In Yangling area, the fruit-grass complex system could store soil water, but would increase the consumption of deep soil water in the dry season, so it should be supplemented with irrigation timely.