This work selected ²²²Rn as a natural tracer to study the hydraulic exchange processes between the river water and the groundwater in Hailing section, Taizhou City. Samples of river water were collected from the Xintongyang Canal and samples of groundwater containing ²²²Rn were collected from the study area. The hydraulic relationship between river and groundwater was analyzed quantitatively. Based on a 1-D steady state model and a flow balance model, the groundwater inflow and the river water leakage were calculated separately. The ²²²Rn tracer results show that the groundwater inflow mainly occurred during two sections of the Xintongyang Canal, R3~R4 and R7~R9, and the tributaries had little effect on the ²²²Rn activity of river reach. Besides, there is an interaction between river and groundwater along the river. Furthermore, the results of the ²²²Rn method are consistent with the results in qualitative analysis. The upstream flow and downstream flow are the most sensitive parameters of the 1-D steady state model, while the ²²²Rn activity of river is a relatively sensitive parameter.