Water sources of woody plants in semi-arid or seasonally dry areas of China are little known. This study investigated the differences in water sources for plants due to seasonal changes (wet/transitional and dry seasons) in semi-arid areas. Stable isotope techniques were applied to determine plant water sources in different seasons. The results show that there is generally a switch of water sources from shallow depths in the rainy season to lower depths in the dry season. This study highlights how seasonal changes in climate in semi-arid China affect plant water uptake and suggests that further study with replicated systematic experiments are needed to better understand the responses in water use patterns to changes in environmental conditions in drought-prone areas.