Abstract: In order to study hydrochemical characteristics of Pingzhai Reservoir, the water source of Qianzhong Water Conservancy Project, Guizhou, the test data of 40 reservoir water samples in 2017-2018 and spatial-temporal distribution of hydrochemical characteristics and the major controlling factors of hydrochemical evolution process of groundwater, were analyzed by means of variation coefficient, spatial interpolation and factor analysis. The results showed that:1) The major anions and cations in Pingzhai Reservoir were HCO₃^- and Ca²⁺, and the main hydrochemistry type was HCO₃^--Ca²⁺. 2) Except SO₄^2- and NO₃^-, the ion concentration in dry period was higher than that in wet period. Spatially, the overall ion concentration was greater than that of tributaries in the main stream of Sancha River, and the concentration of Shuigong River was the minimum. 3) Analysis result by Gibbs chart indicated that hydrochemistry characteristics of reservoir water in the study area was mainly affected by rock weathering, and factor analysis showed that the influence sequence on the chemical composition of the reservoir water was as follows:water-rock interaction > human activity > atmospheric precipitation. For the protection of Pingzhai Reservoir, the water source of Qianzhong Water Conservancy Project, it's necessary to control the discharge of domestic sewage as well as the use of chemical fertilizers and pesticides, and improve the management of industrial and mining enterprises in the surrounding areas.