Langjiu geothermal field in Tibet is located in the northeast margin of Himalaya-Gangdisê plate. Carbonate rocks are widely distributed in this region, and incompletely cooled granites become heat sources of the geothermal field. Equilibrium temperature of the thermal reservoirs is between 191.11 ℃ and 213.85 ℃. The surface water in the geothermal field is bicarbonate-calcium type. Thermal spring’s water is chlorine-bicarbonate type in terms of anionic and kalium-sodium type in terms of cationic. The thermal springs TDS is 2 000~2 300 mg/L with the value of Na+/Cl- greater than 1, and the evolution degree of thermal springs is between mature water and immature water, so water-rock interaction has not reached equilibrium.