Cyanobacterial blooms present risks for drinking water safety, public health and landscape, which cause serious economic losses and social problems. To reveal cyanobacteria bloom-forming mechanism is the basis for cyanobacterial blooms prevention. We reviewed the main hypothesis and evidences of the mechanism of cyanobacteria bloom-forming, mainly including environmental factors (nutrients, TN:TP ratio, temperature, trace elements, zooplankton predation, hydrological and meteorological conditions, etc.) and physio-ecological characteristics (pseudo-vacuoles, sheath, CO₂ concentrating, adapt to low light intensity, the storage of nutrients, sunscreen, produce toxins and nitrogen fixation, etc.), then commented the new theories about cyanobacteria bloom-forming mechanism and prospected the future research. The knowledge of understanding one or two key factors that does not clarify the mechanism of algal blooms. The existing theories or hypothesis have still failed to explain the objective laws of the cyanobacteria bloom-forming clearly even though they have played an important role in the practice of prevention and control of cyanobacterial blooms. Cyanobacterial blooms were multiple driven by environmental factors (external factors) with the advantages of its unique physio-ecological characteristics (internal factors). Hence, cyanobacteria could produce enormous biomass and dominate the phytoplankton community, then bloom under water surface under suitable hydrological and weather conditions. Research on cyanobacteria bloom-forming mechanism should also concern the two aspects. It will be the focus of future research on collaborative expression of different physiological and ecological characteristics of cyanobacteria in different environmental factors, thus affecting the occurrence of algal blooms. The research on mechanism of algal blooms will expand towards the micro and macro level. Molecular biology methods will be used to study cyanobacterial physiological processes at the micro level. At the macro level, remote sensing technology will be used to observe biomass spatial-temporal cyanobacteria variation. It is very vital in the future to strengthen the research on the gene expression of cyanobacterial physio-ecological characteristics and environmental factors coupling affect on the cyanobacterial blooms process. The further investigation that should be interested for us: (1) What is the gene expression and regulation mechanism of Microcystis to form colonies? (2) How do environmental factors affect gene expression and regulation process of the cyanobacteria? (3) What are the quantitative relationships between meteorological factors (radiation, wind, rainfall, etc.), the hydrology or the hydrodynamic process and the growth and distribution of cyanobacteria? (4) What are the quantitative relationships between nutrients and cyanobacterial growth or reproduction? Cyanobacteria bloom-forming mechanism researches include three levels: phenomena, processes and causes. To reveal the disciplines of cyanobacterial bloom in phytoplankton community succession, population development, cell activity and molecular mechanism by a large number of phenomena and processes research, will find the real cause of cyanobacterial blooms and provide a theoretical basis, and better governance measures for the prevention and treatment.