Abstract: Three earthquakes of magnitudes over 7 and more than 10 earthquakes of magnitudes over 6 occurred in Tianjin and its vicinity since the 1966 Xingtai earthquake,it provides favorable conditions for studying the circumstance of hydrogeo-chemistry.The authors have approached the features and the hydrogeo-chemistry circumstances of the moderately strong earthquakes on the basis of the data of 392 wells and over 5000 water sampoles,our research explores a new way to determine the potential seismic region by using the method of hydrogeo-chemistry.