The present article described the importance of prevention, forecast and warning of cyanobacteria bloom. The recent progresses of formation and forecast of cyanobacteria bloom were reviewed. Based on the theory of “four phases of cyanobacteria bloom development” and the temporal and spatial distribution of cyanobacteria overwintering, recruitment and bloom formation in Lake Taihu, the processes of cyanobacteria blooms and the dominant ecological factors during their development phases were studied. Field observations and laboratory simulating studies were performed to investigate horizontal distribution and life characteristics during the overwintering period. The threshold temperature for the recruitment of cyanobacteria was about 9 in the field resear ℃ ch. It was found that there was a positive relationship between effective accumulated temperatures and recruitment biomass of cyanobacteria. By the methods of frequency of dividing cells, the calculation of the growth rates in situ showed that the growth rates of Microcystis were from 0.2 to 0.4. The dynamics of vertical distribution of cyanobacteria in the transport process between different lake areas were investigated under different meteorological conditions, and the results supported the viewpoint that bloom formation is a shift in the vertical positioning of the cyanobacteria biomass which previously distributed through the water column, since the coefficients of variation of the vertical cyanobacteria distribution at different depths were negatively related to wind speeds. On the basis of the establishment of key factors and their thresholds of bloom formation, the bloom forecast model and flow chart ofcyanobacteria bloom forecast and warning were established. The bloom forecasts in 2007, 2008 and analysis of bloom trends of 2008 were implemented. The retrospective assessment of the forecast showed that it is possible to forecast the probability, location and extent of cyanobacteria bloom. The future research directions were also suggested.