Water samples were seasonally collected from two sites in Nam Co and twenty-one inflowing rivers around the lake in 2012 and 2013. Seasonal variations of dissolved organic carbon (DOC) and total nitrogen (TN) concentrations were investigated. Results indicated that DOC concentrations of the twenty-one inflowing rivers ranged from 0.763 to 1.537 mg/L, and TN concentrations ranged from 0.179 to 0.387 mg/L. Average DOC concentrations reached higher values in the late spring and summer, but lower values in winter. TN concentrations showed a contrasting seasonal variation with DOC concentrations. DOC and TN concentrations in Nam Co were 2.42-8.08 mg/L and 0.237-0.517 mg/L, respectively, and seasonal variability of DOC concentrations in lake had same trend as those in inflowing rivers, while TN concentrations showed slight seasonal changes. The seasonal and spatial variations pattern of river DOC concentrations were controlled by recharge modes, while these DOC concentration patterns in the lake are influenced by hydrophyte, algae and exogenous inputs. Meanwhile, the decomposition of DOC and other organic matter significantly influenced the TN concentrations of rivers and lake water column in Nam Co catchment.