There are 25 tributaries carrying significant water and nutrients into Lake Qiandao. As the largest tributary, Xin'anjiang has remarkable impacts on water capacity and water quality of Lake Qiandao. In order to provide substantial information for the exact annual amount of water and nutrients from Xin'anjiang, the inflow volumes during 2006-2016 were calculated based on a catchment model-Xin'anjiang Model. The annual external loadings including total nitrogen (TN), total phosphorus (TP), ammonia (NH₃-N) and chemical oxygen demand (COD_Mn) were further calculated with monthly-monitored TN, TP, NH₃-N and COD_Mn at Xin'anjiang in the same period. For investigating the impact factors of external loading from Xin'anjiang, statistical analysis was conducted with the external loadings correlating the water quality parameters, inflow volume at Xin'anjiang, the population, GDP, economic development and land use at the catchment. The results show that Xin'anjiang is carrying about 51.4% of the total inputted lake water including surface water, ground water and precipitation, accounting for 67.3% of the total water input by the main 25 tributaries. The annual loadings of COD_Mn, TP, TN and NH₃-N from Xin'anjiang are 11458.4 t, 214.9 t, 7649.2 t and 756.5 t which account for 50.7%, 34.3%, 63.7% and 48.4% of the total annual loading from catchment respectively. During 2006-2016, there was an increasing trend of loading COD_Mn, NH₃-N, TN and TP by Xin'anjiang. The external loadings from Xin'anjiang in spring and summer were higher than those in autumn and winter for all parameters. Statistical analysis shows that the COD_Mn, TN and TP loadings are positively correlated with the catchment GDP. The non-point sources from agriculture in Huangshan City have a significant impact on the Xin'anjiang TN loading. The riverine inputs of TP, TN and NH₃-N from Xin'anjiang are having remarkable influence on water quality and ecosystem health at Lake Qiandao.