Dissolved organic matter (DOM) is one of the important components in lake sediment. Identifying the composition and sources of sediment DOM exerts great significance on the understanding of carbon biogeochemical processes and the eutrophication control of lake. To trace the source of sediment DOM in Lake Kulipao, samples of sediment and potential sources were collected in May and August 2021, including surface and core sediment samples, phytoplankton, macrophytes, C3 and C4 plants, livestock manure and treated effluent. Stable isotope (δ¹³C and δ¹⁵N) and fluorescence spectroscopy were applied to characterize the DOM composition of sediment and source samples. Furthermore, contribution rates of different sources to surface and core sediment DOM were calculated using IsoSource software. The calculation results showed that: (1) δ¹³C and δ¹⁵N of DOM in surface sediment differed in May (average values of -25.54‰ and 9.02‰) and August (average values of -26.81‰ and 8.40‰). (2) δ¹³C and δ¹⁵N of DOM in core sediment differed in depth, with average values of -26.58‰ and 9.04‰ in depth of 0-3 cm and -25.40‰ and 10.61‰ in depth of 3-30 cm. (3) Fluorescence components of surface sediment DOM were dominated by humic-like component (87.89%) in May, with HIX and BIX values of 6.27 and 0.67. In August, protein-like component increased to 49.58% with HIX and BIX values of 1.72 and 0.87. (4) Source analysis showed that allochthonous DOM (61%) dominated in surface sediment in May, with soil and treated effluent proportions of 21.40% and 18.08%, respectively. In August, proportion of autochthonous DOM increased to 55.10%, with a high contribution of emergent macrophyte (48.68%). (5) The DOM sources of core sediment showed no significant variation with depth, with treated effluent, submerged plant/algae and emergent macrophyte dominating the DOM with proportions of 42.13%, 25.07% and 18.53%, respectively. In a whole, sources of sediment DOM in Lake Kulipao were mainly related to the human activities and climate features. This study can potentially improve the understanding of DOM accumulation and transportation in northeast watersheds of China.