[Objective] The Characteristics of water quality variation and its impact factors were analyzed in Hulun Lake to provide theoretical basis for the eutrophication mechanism of Hulun Lake. [Method] Monitoring data from 2012-2014 were used to analyze the spatio-temporal distribution of chlorophyll a (Chla), TN and TP. Integrated nutritional status index method was use to evaluate the eutrophication of Hulun Lake and the main impact factors were discussed.[Results] Temporal concentrations of Chla, TN, TP ranked as: July, August > September > January, and the spatial concentrations of TN and TP ranges were 1.70~2.31, 0.15~0.25 mg/L, with their averaged values of 1.94 and 0.19 mg/L, respectively. The water quality of Hulun Lake belonged to levels Ⅳ to Ⅴ according to the water standards of surface water, and the lake was phosphorus limited lake.The concentrations of Chla, TN at southeast, northwest corner were greater that at midle part. Except that one sampling point showed a little high concentration of TP, no obvious spatial variation was found for other points. The eutrophication of Hulun Lake was thought moderate in Summer, but light in Autumm and Winter. [Conclusions] The Hulun Lake has been in eutrophication, this is a result of rich exogenous inputs in non-frozen period.