Abstract: In order to investigate the spatial and temporal variations of hydro-chemical characteristics and its controlling factors in humid regions of southern China, water samples were collected from the Beijiang River and its tributaries in June and December 2015, respectively. Based on chemical parameters and major ions concentration, the chemical weathering and ions fluxes were estimated by the stoichiometry and mass conservation to identify the effects of natural and anthropogenic processes in the basin scale. The result showed that (1) The concentrations of main ions were higher in the non-flood season than that in the flood season. The geological features and mining activities affected greatly the chemical components in the river waters, resulting in the hydrochemistry type as Ca-HCO₃ in the Beijiang River and Lianjiang River, and Ca-SO₄ in the Wengjiang River. (2) The contribution of rock weathering to river chemistry is in the order of carbonate minerals (78.44%) > silicate minerals (14.43%) > precipitation (5.42%) > evaporite (1.71%). Since carbonatite is the main rock found widely in the basin, the mining activities accelerated dissolution of carbonatite, accounting about 7% of the total chemical weathering in the Beijiang River Basin. (3) The weathering rates of Beijiang River Basin were 7.49 t/(km²·month) in the flood season and 5.29 t/(km²·month) in the non-flood season, with the rate of 87.63 t/(km²·a). The annual chemical weathering rate in the Beijiang River is similar in the Xijiang River, but much higher than the Dongjiang River even the global average of rivers. Therefore, the chemical weathering in Beijiang River is very important for hydrochemistry in the Pearl River basin.