This paper deals with geochemical characteristics of alkali metal elements in soils of the Yangbajing high-temperature geothermal field and its neighboring area of 90 km². Studies show that alkali metal elements Li, Kb and Cs can serve as a set of new geochemical indicators for the thermal field exploration and the delineation of thermal field limits,and their function is similar to that of such geochemical indicators as Hg, As, Sb and Bi. Apreliminary discussion is made concerning the distribution and geochemical behavior of alkali metal elements in geothermal system and the cause for the formation of anomalies. Correlation analysis demonstrates that these geochemical indicators have intimate correlationship, suggesting their common origin. Using Na and K. in the thermal water as geothermal temperature indexes, the authors have made an estimation of the temperature of underground hot water in the Yangbajing thermal field.