Testing and analyzing the samples collected from the upriver tributaries of Ganjiang, we found that the river and its tributaries have low total dissolved solids concentrations and the chemical composition of river water is dominated by Na+, Ca2+, Cl-,HCO3- and Si, representing that of the river water from the typical silicate rock areas. Seawater correction approach (Cl- normalized seawater ratios) was used to estimate the contribution proportions of local precipitation to the solutes, we found that most watersheds of southern Jiangxi province were evidently influenced by precipitation. After the contributions of precipitation deducted from the total dissolved solids, on the basis of the principal composition analysis and factor analysis, the watersheds of Ganjiang were influenced strongly by silicate weathering. At the same time, the watersheds are evidently influenced by evaporates under the influence of the mineral resources. In this paper, the upriver tributaries of Ganjiang were selected for analyzing the dissolved inorganic carbon isotope composition of it. It has δ13CDIC of -8.35 to -13.74‰, with an average of -11.65‰. The key source of DIC is soil CO2 and carbonate weathering. According to carbon isotopic composition of soil CO2 and carbonate rock, 68.5% of the DIC is calculated to originate from soil CO2, respectively, and 31.5% of the DIC is calculated to originate from carbon rock. The soil CO2 consumption of chemical weathering processes is 2.11 ×105 mol/yr·km2, and about 9.6 ×104 mol/yr·km2 is from carbonate. At the same time, the tributaries have different δ13CDIC values each because of different environments and the human interference.