[Objective] The sources and use strategies of soil water absorbed by an oil peony were explored in order to provide a basis for the improvement of the survival rates in rational plantations of the plants and the development of the oil peony industry.[Methods] Two kinds of oil peonies of different ages were used as materials. The ratios of stable hydrogen and oxygen isotopes in the plant and soil water were tested to analyze the sources of soil water absorbed by oil peonies in spring and autumn.[Results] ① Mature individuals of oil peonies developed strong root systems and consequently more optimal strategies of water use than young individuals did. In spring (or dry season), oil peonies with two ages mainly absorbed water from surface soil (0-20 cm). However, mature oil peonies used more water (70.7%) from the surface soil than young ones did (61.8%), comparatively. In autumn (or relatively humid season), there was high water content in the surface soil. Mature oil peonies conversely tended to absorb soil water from deeper layers of soil compared with young peonies. ② On the basis of the analysis of soil water content, the contribution rates of different sources of soil water to the growth of peonies, and their relationships, it was found that the soil layers with high contribution rates of water to the growth of oil peonies had low soil water content.[Conclusion] An oil peony tends to absorb water from soil layers with low water content during spring and autumn. This verifies both the tolerance of an oil peony to drought and its intolerance to waterlogging.