Abstract: This paper is the result of hydrogeologic survey engineering. [Objective]Budongquan spring is in the region of Hoh Xil on the northern Qinghai–Tibet Plateau. It is a typical sub-surface spring with discharge that ascends to the surface through taliks in the permafrost. It is an important water supply for the Qinghai–Tibet railway and the construction of small towns along the railway. Therefore, it is very important to understand its formation and water characteristics. [Methods] In this paper, we evaluated spring water quality using the single index evaluation method. We analyzed water storage, circulation, and sources of main chemical components by examining the local geology, environmental isotopes, and hydrochemistry. [Results] Results show that Budongquan spring water quality is in class V throughout the year. It is in class V in terms of total hardness, SO42?, and Cl?, and in class I–II in terms of toxicological and heavy metal indices. Nearby glacier meltwater and river water are in class I–II. The spring is mainly recharged by glacial meltwater from the southern slope of Kunlun Mountains, atmospheric precipitation, and surface river water. Average cycle length is less than 5–10 years. Groundwater flow follows the talik zone along the northeast-trending active normal faults. Budongquan spring is formed by the surfacing of groundwater that is blocked by the west-northwest-trending active reverse faults. Its chemical composition is mainly determined by evaporation, and presence of and interaction with magnesium salts and carbonate rocks. [Conclusions] To meet standards for drinking water, we recommend mixing spring water with river water at a ratio of 1:2.