Abstract: Analyzed from monthly mean value figure since 1986, the water radon has varied in high value, and a single point anomaly that went beyond 2 times mean square deviation occurred on its first order difference curve in May of 2003.In the analysis of past, the notable change in water radon of Handan well was always attributed to environmental or instrumental affect, but we think this kind analysis is too simple, so the data of the well is thoroughly studied here, and its capacity to reflect earthquakes is discussed.