Abstract: Radon isotope (²²²Rn) is a natural radioactive gas, colorless and odorless, with a short halflife (t_1/2=3.8 days) and conservative chemical properties. Its concentration is higher in groundwater than in surface water. It is sensitive to sudden changes in subsurface geologic conditions, and thus can be used as a desirable tracer in water science research. However, the application of radon tracer technology in the field of water science is still in the primary stage. This review introduces the physical and chemical properties, detection and quantification methods of ²²²Rn. We evaluate the application of ²²²Rn as a tracer in quantifying the interactions between groundwater and surface water, as well as in the research of hydrogeochemistry, water environment monitoring, and hydrogeological exploration. The problems and deficiencies in the application of radon tracers are discussed. The broad prospects for their application in hydrogeochemistry, the mechanism of earthairmatter interaction processes, and water environment monitoring are elucidated. Suggestions are made for the future development of research in this field.

Key words: radon (²²²Rn), radon mass balance, carbon, nitrogen and phosphorus, groundwater-surface water interaction