The effects of nitrogen in different format on the growth,biochemical composition,fatty acid composition and content of Phaeodactylum tricornutum and Tetraselmis Chui was investigated.The results showed that: with urea as nitrogen source,the biomass,growth rate,chlorophyll content,soluble sugar and soluble protein contents of Phaeodactylum tricornutum were the highest,followed by sodium nitrate and ammonium chloride as nitrogen source.However,with ammonium chloride as nitrogen source,total lipid content was the highest,and types of fatty acids were the most.Tetraselmis Chui with ammonium chloride as nitrogen source,the biomass,growth rate,chlorophyll content,soluble sugar and soluble protein contents were the highest,followed by urea,sodium nitrate.However,the total lipid content and fatty acid species reached their maximum with sodium nitrate as nitrogen source.