The concentrations of dissolved organic carbon （DOC） and nitrogen （DON） in water bodies were continuously monitored from July 2019 to May 2020 in Nantiaoxi river （an important tributary in the upper reaches of the Taihu Lake Basin） Watershed. We explored the temporal and spatial variations in DOC and DON concentrations of water and revealed the associated driving mechanisms. The results showed that the mean water DOC and DON concentrations in the watershed were （2.57±0.09） and （0.40±0.01） mg·L^-1, respectively, and the mean DOC/DON ratio was 9.43±0.46. The highest water DOC and DON concentrations appeared in summer, and the DOC/DON ratio in spring and autumn were significantly higher than that in summer and winter. The DOC concentration increased with increasing chlorophyll a （Chl-a） and nitrogen concentrations, while DON concentration was positively correlated with granular nitrogen （PN） concentration. The highest water DOC and DON concentrations in summer were probably due to the release of more DOC and DON from the higher primary productivity of phytoplankton, which was likely caused by the favorable condition of high rainfall, air temperature and a high concentration of nitrogen pollutant in summer. The water DOC concentration and DOC/DON ratio in agricultural and residential regions were significantly higher than those in forest region during the study period, and water DON concentrations in agricultural region were significantly higher than those in forest and residential regions. Our findings indicated that water DOC from forest region was mainly generated by endogenous pathway and possessed higher bioavailability, while the proportion of exogenous DOC in water from agricultural and residential increased, and water DON in these two regions had higher bioavailability. The spatial variations were mainly mediated by anthropogenic activities, i.e., the pollutant discharge from agricultural and residential activities could increase water DOC concentration and DOC/DON ratio in these regions, while agricultural activities such as fertilizer and manure application were the main reason for the higher water DON concentration in agricultural region.