Abstract: Studying the change and response of lake water quality driven by natural and human factors can provide a scientific basis for water environmental management. This study accessed the effects of different scenarios of pollutions reduction on water quality using the combination methods of twodimension water quality numerical modelling and greymode identification accessing. Based on measured topography, hydrological, meteorological data and water quality in 2012, as well as the quantitative results of pollution resources, a twodimensional hydrodynamic and water quality coupling model of Honghu Lake was established. The pollution resources were generalized to surface runoff, aquaculture activities and atmospheric deposition. The results showed that, during the model calibration and validation periods, the average water level RMSEs were respectively 0.10 m and 0.08 m, the concentration RMSEs of total nitrogen, total phosphorus, ammonianitrogen and permanganate index were respectively 0.171 mg/L, 0.009 mg/L, 0.110 mg/L, 0.627 mg/L and 0.191 mg/L, 0.020 mg/L, 0.079 mg /L, 0.689 mg/L. The simulation results meet the accuracy requirements of water quality model. The water quality change under different scenarios of load reduction revealed that under 50% reduction of inflow loads, the decreasing rates of total nitrogen, total phosphorus, ammonianitrogen and permanganate index concentration were largest, which were respectively 37.2%, 35.1%, 37.3% and 37.2%. The comprehensive water quality index were decreased from the baseline (2.84) to 2.44. The areas of grade V water quality did not exist. The percentage in areas of grade IV water quality decreased from 15% (baseline) to 10%. The areas of grade III water quality accounted for 90% of the whole lake area. it concluded that the water quality deterioration primarily was owing to nonpoint pollution from upstream Sihu watershed brought by runoff. We should vigorously develop nonpoint source pollution control in the upstream and carry out the ecological restoration in the northeast and northwest of Honghu Lake.