Abstract: Taking Chaohu Lake as the study area, potassium permanganate index (COD_Mn), total nitrogen (TN), total phosphorus (TP),Chlorophyll-a(Chla),pH data in the 12 monitoring points of the lake and the corresponding temperature,radiation, etc. (from 2000 to 2007) from China Meteorological Administration were collected. Through the mutation discrimination, TP was selected as state variables,COD_Mn and temperature, ratio of nitrogen to phosphorus(N/P) and pH, N/P and radiation were decided as control variable,then three water bloom catastrophe models were constructed by 12 lake monitoring points data. The obtained cross set equation is B=8P³+27Q², which can be as criterion equation of water bloom outbreak. When valued in critical near zero or less than zero, then the water bloom would appear,aquatic ecosystems in the state of mutations, we should complete water bloom outbreaks of emergency response plan. Model testing and monitoring data consistency is good.