Abstract: The authors analyzed characteristics of organic carbon content and isotope distribution of top soil in different Land use types within the Taihu Lake basin, as well as surface sediments and organisms within the estuary. The sources of organic matter of lake sediments were obtained by using two-member mixing model. The results showed that there were differences of organic δ¹³C in different plant types, which affected organic δ¹³C of top soil within the catchment. The average δ¹³C_org values of tea plantations, vegetable lands, forest lands and paddy fields were -25.4‰,-25.8‰,-27.1‰ and -28.1‰ respectively,and the highest δ¹³C_org value existed in tea plantations. The range of δ¹³C_org values of surface sediments within the estuary were -27.5‰~-25.1‰ with the average value of -25.7‰. The δ¹³C_org of surface sediments near the shore was low, and gradually decreased from the estuary to center. The reason was the effect of import of terrestrial source with lower δ¹³C_org values. By using two-member mixing model, the contribution ratios of terrestrial source was 70%~80% in the estuary, and gradually decreased with the distance to the lake shore.