Based on the analyses of temperature field in subsurface geothermal reservoir aud un-derlying granitic batholith of the Yangbajing Geothermal Field, both the difference in res-servoir eharacters of the northern and southern parts of the field and their identity in heatervoir characters of the northern and southehave been ascertained. Furthermore, it hasbeen establishedt hat the Nyainqentanglha and Tanggulashan piedmont fault zones are thecontrolling structures for the boundary of the geothermal field; meanwhile, the distributionof lithological character of the Quaternary system in the reservoir is the main controllingfactor for the geothermal reservoir behaviours. In accordance with the temperature datafrom the deep drill holes in the geothernml field, a heat transfer model down to a depth of3.3 km in basement rocks has been worked out. Using the principles of transient heat trans-fer and heat balance a rough estimate has been obtained that the last hydrothermal fluidinjection into the geothermal reserv Based on the analyzes of temperature field in subsurface geothermal reservoir aud un-derlying granitic batholith of the Yangbajing Geothermal Field, both of difference in res-servoir eharacters of the northern and southern parts of the field and their identity in heatervoir characters of the northern and southehave been ascertained. Furthermore, it has been established that the Nyainqentanglha and Tanggulashan piedmont fault zones are thecontrolling structures for the boundary of the geothermal field; meanwhile, the distributionof lithological character of the Quaternary system in the reservoir is the main controllingfactor for the geothermal reservoir behaviors . In accordance with the temperature data from the deep drill holes in the geothernml field, a heat transfer model down to a depth of 3.3 km in basement rocks has been worked out. Using the principles of transient heat trans-fer and heat balance a rough estimate has been obtained that the last hydrothermal fluid injection into the geothermal reserv