Abstract: Better understanding of water pool dynamics and complex interactions among waters in precipitation, plant, soil and aquifers, as well as watershed output remains as one of the most challenging tasks for today’s ecohydrological research. Stable isotope “Two Water Worlds” (TWW) hypothesis, proposed about 10 years ago, provides a new pathway to quantifying the dynamics of these complex interactions. Although TWW hypothesis is well supported by many studies, its effectiveness is still under serious debates. In this review, we highlight significant advances on the current applications of this hypothesis to the research of ecological hydrological processes including water isotope fractionation of SPAC system, isotope exchange of soil water flow, isotope exchange of plant water uptake and transport processes, plant-soil water interactions, and the major limitations after introducing briefly the history of TWW hypothesis development and its context. We also provide some suggestions for future research directions, aiming at promoting applications of stable isotope techniques to ecohydrological research in China.