The community structure in the Tianshan Mountains is relatively simple and there are a few woody plant species. However, the water competition pattern among the main woody plants in the shrub community of the Tianshan Mountains is not clear due to lack of the quantitative analysis related to water use dynamics of the shrubs. The hydrogen and oxygen stable isotope composition of xylem water of four main shrubs and their potential water sources in the shrub community in the study area were measured in this paper by using stable isotope technology. In order to explore the differences and dynamics in water sources of main shrub species in shrub community of Tianshan Mountains, the IsoSource model was used to analyze quantitatively the relative contributions of each potential water source used by the four shrubs in summer. The results showed that in July, when 0-20 cm shallow soil water content was sufficient, Rosa spinosissima, Cotoneaster melanocarpus and Spiraea hypericifolia extensively extracted shallow soil water, and the relative utilization ratio was higher than 89.3%. On contrary, Berberis heteropoda absorbed water from all the potential water sources (30.7% of shallow soil water, 29.4% of middle soil water, 25.7% of deep soil water, 14.2% of stream water, the same below); In August, when the water content of the shallow soil decreased, the Rosa spinosissima converted to 60-100 cm deep soil water and stream water, and the relative utilization ratios were 64.8% and 27%, respectively. Cotoneaster melanocarpus and Spiraea hypericifolia extracted water from all the potential water sources in similar proportions (33.8% and 36.8%, 30.9% and 29.7%, 23.5% and 22.3%, 11.8% and 11.2%). Berberis heteropoda relied mainly on the stable deep soil water below 80-100 cm; In September, when the shallow soil water content increased, all of the four shrubs absorbed large amount of shallow soil water, and the relative utilization ratio was higher than 72.2%. This indicates that the main tree species of the shrub community in the Tianshan Mountains could convert the plasticity of the water sources to deal with the environmental water variation, by dividing the water sources in time and space to reduce the pressure of competition on water resources, which would promote the coexistence of species through niche differentiation in water resource utilization.