An experiment that Microcystis aeruginosa was exposed to short-term (0-24h) simulated UV-B radiation was carried out to determine the effect of increased UV-B radiation on the phytoplankton growth in lakes, especially lakes in the mountain and plateau.By measuring the biomass, physiological and ultrastructural indices, the response of M.aeruginosa to UV-B radiation was analyzed.When the UV-B radiation exposure time reached to lh, the M.aeruginosa began to die, but the protein concentration increased and chlorophyll-a concentration remained stable.When the UV-B radiation exposure time was less than 4h, the activity of superoxide dismutase (SOD) enzyme remained high, the cell membrane was in good condition, and the number of thylokoids and cyanophycin granules remained stable.When the UV-B radiation exposure time was more than 4h, chlorophyll-a concentration and the activity of SOD enzyme of M.aeruginosa started to rapidly drop.The UV-B continuous radiation exposure time reaching to 4h was the maximum resistance of M.aeruginosa.