A strain of microalgae rich in carbohydrates named WZKMT was got from Wuhan Botanical Garden,Chinese Academy of Sciences,and identified as Scenedesmus sp.by morphological properties.Then,molecular identification were examined and the result showed this speices clustered with Scenedesmus raciborskii was identified as Scenedesmus raciborskii WZKMT.Nutrient limitation strategy was used to study the effect of nitrogen concentration on starch content.Five BG11 mediums with different NaNO3 concentration were designed for microalgae cultivation,carbohydrates and strach content was analysised every 24h.This study found that the method of nitrogen stress has little influence on total sugar and starch content,the higest total sugar and starch content were about 65%and 50%respectively.The high carbohydrates and starch content suggests Scenedesmus raciborskii WZKMT as a very promising feedstock for bioethanol.