Abstract: The sediment columns in the estuary of Laoyu River in theDianchi Lake watershed were taken as the object of the study to analyze the distribution characteristics of n-Alkanes and TOC.The sources of organic matters can be tracked on the basis of the relevant indexes of n-alkanes.The results showed that the organic sources were the herbaceous plant from ancient time.As time went by,woody plant had become the main source,and at the present time,alga and fossil fuel made more contribution to the organics in the sediment than before.