Abstract: Abstract：In this study, the surface and groundwater samples of Banzhai River, in Libo Nature Reserve, Guizhou Province were collected; the contents of main anions and cations and stable carbon isotopes of HCO3- were measured.The hydrochemical characteristics of Banzhai watershed in different seasons were analyzed, and the source of water solutes and the hydrochemical processes were discussed based on the isotope values of δ13C.The results showed that the main anions of the watershed were HCO3- and SO42- which accounted for 86.15% and 10.37% of the total anion equivalent respectively, while the main cations of Ca2+ and Mg2+ accounted for 76.92% and 20.50% of the total anion equivalent respectively.The relatively large amount of Mg2+ in river water indicates that it may be partly derived from dolomite weathering.The relatively higher SO42, K+ and Na+ in the groundwater of school sampling sites indicated this site may be influenced by anthropogenic sources.The δ13C values of DIC in Banzhai watershed ranges from -16.87‰ to -10.80‰, which is negative in summer and positive in winter, and there is a negative correlation between HCO3- content and its value of δ13C, which may be the result of the combined action of temperature and precipitation intensity in different seasons.There is a significant positive correlation between SO42- content and theδ13C values of DIC, which indicates that H2SO4 may be contributes to the weathering process of carbonate rocks in Banzhai watershed.