In this paper,based on the subordinate function method and adaptive threshold method,the Ca²⁺ and Cl^-concentration monthly observation data of Yancheng Yanfang Mill in Jiangsu Province were analyzed and anomalies before earthquakes were extracted. Combined with wave velocity ratio and geomagnetic harmonic amplitude ratio data,the mechanism of reflecting earthquakes was discussed by the dilatancy-diffusion model. The results show that from 2008 to 2016,Ca²⁺ concentration has 6 subordinate function anomalies and 5 adaptive threshold anomalies,Cl^- concentration has 4 subordinate function anomalies and 5 adaptive threshold anomalies,which correspond well to earthquakes of local magnitude above 4.0 within 200km of epicenter distance form the station. In addition,according to the results of wave velocity ratio,geomagnetic harmonic amplitude ratio and geochemical origin of groundwater,it is judged that the rapid rise of Ca²⁺ and Cl^- concentration before earthquakes are related to the upwelling of deep fluid.