Abstract: Study on the hydrochemical characteristics and formation mechanism of geothermal water can provide the hydrogeochemical basis for the exploitation and protection of geothermal resources. The insufficient research of hydrochemical formation mechanism is a limitation in the development of geothermal water in northern \mbox{Ji’nan}. Water samples were collected in southern Karst and geothermal wells in this paper. Methods including \mbox{Piper’s} triliner diagram, correlation analysis, ion ratio, mineral saturation index and the inverse geochemical modelling were employed to analyze the hydrochemical characteristics and formation mechanism. The results show that from south to north, the concentration of TDS and main ion content showed a rising trend, and the groundwater chemical types change from HCO\textsubscript{3}{\hyphen{}}Ca to HCO\textsubscript{3}{\hyphen{}}Ca$\cdotp $Mg, SO\textsubscript{4}{\hyphen{}}Ca, SO\textsubscript{4}{\hyphen{}}Ca$\cdotp $Na showing zoning characteristics. Carbonate, sulfate minerals and halite mineral dissolution{\hyphen{}}precipitation in this area were the dominant hydrogeochemical processes to control the groundwater chemical characteristics, accompanied by the dissolution of albite, K{\hyphen{}}feldspar and other silicate minerals. However, southern cold water is affected by a certain degree of human~activity.