The reliability of anomaly of water-radon in Dingxiang spring observation in 1996 is discussed, based on data of the hydrogeologic condition at the spring, the characteristics of water-radon anomaly and the normal influence fectors from environment. It is considered that the anomaly of water-radon not only correlates with air temperature and waterfall, but also with variation of stress-strain in rock, is the reliable precursor anomaly before Zhangbei M 6.2 earthquake in 1998.