Lake Tongting area has a dynamic water environment with developed surface water networks, complex hydrogeological conditions and intensive human activities, which makes it difficult to gain in-depth understanding of groundwater storage and movement in the lake area. This study applies dynamic analysis of water levels and radon (²²²Rn) tracer method to carry out qualitative and quantitative analyses of surface water-groundwater interaction and exchange fluxes in Lake Tongting area in the dry season. The spatial distribution patterns of water levels and ²²²Rn concentrations in the lake area in the dry season (between 2018-2020) indicated that groundwater (GD) discharge to the lake occurred in the dry season, especially in eastern Lake Dongting. According to calculation using radon box model, the GD-borne ²²²Rn flux in the dry season was 455.09 Bq/(m²·d), or 60.07% of total ²²²Rn flux to the lake; the total groundwater discharge was 0.29×10⁸ m³/d, and the average discharge rate was 56.27 mm/d. Groundwater discharge contributed to 7.04% of surface water in the dry season. Sensitivity analysis showed that sensitive variables in the model were wind speed, ²²²Rn concentration in groundwater/lake water and surface area. Improvements of sampling scheme and measurement accuracy of sensitive variables can improve reliability of calculation results. With clear physical significance and simple application protocol, radon (²²²Rn) tracer has certain application advantageous that it can be effectively used to quantify groundwater recharge, runoff and discharge in complex water environments. The research results provide better understanding of water balance in Lake Dongting and can serve as reference for water resource evaluation and management in the lake area.