The features of Hydrochemical precursory fields of the Tangshan and Songpan Ms>7.0earthquakes have been studied. The results show that the precursory fields of the two earthquakes have the similar property. The proportion of long-term and imminent anomalies to all anomalies is inversely proportional to epicentral distances. The long-term and imminent anomalies in the focal areas emerge earlier than those in the area far away from foci. All thelong-term anomaly patterns show gradually rising. The formation of hydrochemical precursory field has something to do with regional stress field,but has even closer relation with focal stress field. Focal stress field in the precursory process may play a main role.