In order to provide a theoretical basis for ecological monitoring and evaluation of lakes using biofilm, the effects of duck wastewater with different concentration gradient on the biomass and extracellular enzyme activities of biofilm were studied by microcosmic experiment. The results showed that duck wastewater significantly increased the biomass of biofilm. In short-term exposure, the biomass of biofilm(chlorophyll a and ash-free dry weight )was linearly correlated with the concentration of duck wastewater, while in long-term exposure, it was in accordance with Logistic equation, which indicated that the duck wastewater had saturation effect on the promotion of biofilm biomass. The effect of duck wastewater on extracellular enzyme activity of biofilm was affected by exposure time. The activities of alkaline phosphate(APA), glucosidase(GLU)and leucine peptidase(LAMP)were increased by short-term exposure(24 h). The activities of these three enzymes increased logarithmically with the increase of the concentration of duck wastewater. While in the long-term exposure(60 days), the activity of three kinds of enzymes were inhibited by duck wastewater, which decreased logarithmically with the concentration of duck wastewater.