On the basis of collecting the groundwater chemistry analysis data of Qilihai emergency water source field in Tianjin, the paper applied Piper diagram, scatter diagram and Gibbs semi-logarithm picture to study the formation mechanism of groundwater and fluoride. The results showed that the main type of water chemistry is HCO3—Na, and partially is HCO3·Cl—Na, the major chemical process of groundwater mechanism is controlled by rock weathering and evaporation-crystallization; Ca2+ can inhibit the release of fluoride in water. Besides, results from the inverse modeling of hydrogeochemistry reactions in the Ⅴ aquifer indicate that deep groundwater has mainly experienced the processes including the dissolution of dolomite, calcite， gypsum, halite and fluorite.Accompanied by the effect of cation exchange, the mineralization degree is significantly increased, the type of groundwater chemistry is turned from HCO3—Na to HCO3·Cl—Na.