Morphological and taxonomic character of bloom-forming cyanobacteria in Aixi Lake were first reported in this study. The community characteristics and diversity of bloom-forming were analyzed. The distribution of these cyanobacteria in China and toxin producing ability were discussed. Several cyanobacteria-blooms were found in different area of Aixi Lake in 2016, cyanobacteria became the absolutely dominant species, while the diversity of phytoplankton decreased. This phenomenon gave rise to the inhibition in the reproduction of other phytoplankton. Samples were obtained and analyzed by microscope. 7 dominant bloom-forming cyanobacteria were identified in the samples, they were Microcystis wesenbergii, Microcystis novacekii, Planktothrix isothrix, Planktothrix spiroides, Planktothricoides raciborskii, Cuspidothrix issatschenkoi, Dolichospermum compacta. The diversity of bloom-forming cyanobacteria was high in the Aixi Lake. Remarkable seasonal succession of dominant bloom-forming cyanobacteria was found in Aixi Lake, Microcystis is the dominant bloom-forming species in spring; Planktothrix spiroides and Planktothricoides raciborskii were dominant species in summer. Several species of bloom-forming cyanobacteria in Aixi Lake can produce microcystins and neurotoxins etc., indicating that severe threat in water security of Aixi Lake will be caused by these species.