Abstract: Abstrac This article focuses on an anomaly observed by the radon - thorium analyzer in Wen'an Well. It exhaustively records the workflow of grassroots stations in verifying fluid anomalies, covering aspects such as basic data collection, instrument condition inspection, and surrounding environment investigation. Through on - site sampling, the hydrochemical data of Wen'an Well are obtained for the first time. It is determined that its hydrochemical type is HCO3 - Na+ type water, and the analysis shows that the recharge sources include the mixing of shallow - surface substances and deep - groundwater recharge, with water - rock interaction occurring and no ionic equilibrium reached yet. The study comparatively analyzes the underground fluid data, seismic activity, hydrochemical data, parallel observation data, and morning - afternoon comparative observation data of Wen'an Station, ruling out influences such as instrument malfunctions, environmental interference, and meteorological factors. It is comprehensively determined that the high - value anomaly of radon in Wen'an Well since May 17, 2024, may be related to the enhanced regional stress. This research provides technical support and analytical ideas for the verification of earthquake precursor anomalies, and has important reference value for the research of underground fluid disciplines and earthquake monitoring and early warning.