The biological characteristics and competitive predominance of cyanobacteria, as well as the formation and maintenance mechanism of cyanobacteria blooms, have aroused continuous interests among researchers. As an important nutrient for cyanobacterial growth, the assimilation of nitrogen is intimately coupled with the photosynthesis. However, nitrogen exists in various chemical forms in water, which affect the cyanobacterial growth and the formation of blooms in distinct ways. To delve into the formation mechanism of cyanobacterial blooms, it is important to understand the cyanobacterial photosynthetic feature as well as the mechanism and strategy by which the nitrogen of different forms are assimilated into cyanobacteria. This paper reviewed the processes and characteristics of photosynthesis in cyanobacteria, such as light energy capture and excitation energy transfer, primary photosynthetic reaction, CO₂ concentrating mechanism and assimilation. Then, it illustrated the transport and assimilation of different nitrogen forms (NO₃^-, NO₂^-, NH₄⁺, urea and N₂), the regulation of these processes, as well as the mechanisms by which cells coordinate and regulate the carbon/nitrogen metabolism. The paper also summarized the latest research advances in cyanobacterial blooms and suggested on the content and direction of further research.