The high temperature adaptation of some fresh water cyanobacteria is discussed in this paper.Six possible mechanisms for adaptation of these fresh water cyanobacteria to the high temperature have been proposed on the basis of correlating references, i.e.(1) different species of fresh water cyanobacteria have slightly different morphonogical adaptations; (2) the thylakiod membrane of these fresh water cyanobacteria has a higher thermostability; (3) these fresh water cyanobacteria produce heat shock proteins when they are in heat stress in case the enzymes are denatured; (4) the photosystem of these fresh water cyanobacteria has a higher thermostability; (5) the thermostability of DNA of these fresh water cyanobacteria plays a key part during the process of metabolism; (6) there exists a stable protein synthesizing system in these fresh water cyanobacteria.The adaptation for these fresh water cyanobcteria under high temperature is due to the coordination of the factors mentioned above, among which the thermostability of DNA and protein synthesizing system, the gene manipulation play an insubstitutable role during temperature variation from the lower growth limits to the higher ones.