Two kinds of marine microalgae,chaetoceros gracilis and platymonas subcordiformis which have high economic value as research object,are setected to do the culture experiment in incubator with light red,green,blue,white-LED spectrum of different combinations compareing with the traditional fluorescent. By comparing the growth rate with the fluorescent light,it′s showed that LED light source spectral composition is more effectively to promote the growth of microalgae. The obvious advantages of LED as light source of microalgae are indicated.