Content of total organic carbon in lake sedim ents is usually used to obtain the lake paleoprimary productivity．Such organic matter will conduct a series of chemicaI and biological reaction after it deposits in the lake bo ttom． Therefore the total organic carbon in lake sediments only offers rough information about lake paleoprim ary productivity． Based on the content of total organic carbon and the organic 8 C of the sedim ents．the source of sediment has been distinguished． By analyzing the pigment index， the environmental evolution history of the lake has been recovered， These researches made it clear that Nana ihu Lake has formed in 2，45kaBP with the lake water mainly coling from the Yellow River． The deposition environment of the east part of the lake is different from that of the west， In the west part(W eishanhu Lake)the sediments mainly com e from the flood plain materials of the Yellow River．while in the east part (Dushanhu Lake)the sediments mainly come from the footslope materials，Recently，the Cyanophyta is flourishing in the lake and the lake gradually comes into the eutrophication stage.