M. aeruginosa Kutz is harmful to ecological environment of lakes.The algae in water bloom of Dianchi Lake was isolated with methods of dilution and agar solid-media culture.It was found that after purification, grow thing rate of the algae was raised by 5 times in liquid culture media.When extracting total DNA of the algae, if the cells were pre-treated by alcohol + ether (1:1), their gelatinous sheathes were broken and the production of total DNA increased by 3-4 times.The improvement of DNA ex traction is useful to molecular biology studies of the algae.