Surface water samples from the Maolan National Natural Reserved Park (MNNRP) were analyzed from Sept. 2013 to June 2014, for major ion concentrations (K+, Na+, Ca2+, Mg2+, Cl-, SO42-, HCO3-), delta C-13-DIC and delta S-34-SO4(2-) to quantify the sources of solutes and chemical weathering. The results show that HCO3- and SO42- are the main anions in Banzhai watershed, which account for 86.2 and 10.4% of the total anion equivalent, respectively. While Ca2+ and Mg2+ account for 76.9 and 20.5%, respectively. Considerable Mg2+ in stream water indicates that it may be affected by dolomite weathering. stream water samples present the delta C-13-DIC values in the range of -16.9 parts per thousand similar to-10.8 parts per thousand (mean value was -13.9 parts per thousand), which were lower than that of the groundwater. The delta S-34-SO42- values ranged from -15.2 parts per thousand to 1.7 parts per thousand (mean value was -4.4 parts per thousand). There was a negative correlation between HCO3- content and delta C-13 value, implying the result of the interaction of temperature and precipitation intensity in different seasons. The significant positive correlation between SO42- content and delta C-13-DIC indicates that H2SO4 may be involved in the weathering process of carbonate rocks in small watershed scale. The content of SO42- in a school sample site was much higher than that of other sample sites for the interference from human sources. The delta S-34 values show that the average delta S-34-SO42- in most sites is close to the delta S-34 isotopic values of Guizhou coal and rain, indicating that they may be affected by local coal.