According to MONERIS, three models were established to estimate the nutrient emissions into the river systems of the southwestern Taihu Basin, i.e, a nutrient balance model of the agricultural land, an emission model that was used for the estimation of nutrient emissions from catchments to river systems, and a riverine retention model that was used for the estimation of nutrient loads from emissions. The comparison of the calculated loads with the observed loads shows a deviation as low as 10% and 30% for nitrogen and phosphorus, respectively. It was estimated that the nitrogen input into the river system amounts to about 5645 t/a in the period 1997 - 2001. These emissions have decreased since the former five years by about 827 t/a. For phosphorus the emissions have reduced by 45 L/a and amount 554 t/a in the period 1997-2001. Analysis of the results show that the decrease of the nutrient emissions are mainly caused by the great reduction of nutrient surpluses from the agricultural land and the emissions from point sources.