Abstract: Lakes’eutrophication become a serious environmental problem in China,and the algae bloom is the challenge of all the eutrophicated lakes.Pollution sources of eutrophication lakes include external sources and internal sources.When the external pollution sources are controlled,eutrophication will still happen because of the existence and release of inner loading nutrient in sediments.Then nutrients become the leading factor of the lakes’ eutrophication.The mass concentration of total nitrogen (TN),ammonia (NH4+-N),nitrate (NO3--N) and organic nitrogen (ON) in interstitial water and overlying water of Dianchi lake was mensurated.The results are as following:① No matter in Caohai or Waihai,the mass concentration of TN,NH4+-N and ON are higher in interstitial water than those in overlying water,which indicates that the nitrogen in the sediment has been releasing into the water column and play an important roll in the eutrophication process of Dianchi Lake.So more attetion should be paid to the internal pollution sources when controlling the eutrophication of Dianchi Lake.② The mass concentration of TN,NH4+-N and NO3--N are higher in Caohai than those in Waihai,so it can be conclude that the pollution degree of Caohai is more serious than that of Waihai.The spatial distribution characteristics of nitrogen and the rolls of internal sources in lakes’ eutrophication are explained clearly from the research.