Abstract: The total organic carbon (TOC, 6.7%), total nitrogen (TN, 0.6%), δ¹³C_org (-28.0‰), δ¹⁵N_total (2.2‰), aliphatic hydrocarbons, fatty alcohols, fatty acids and glycerol two alkyl glyceryl ether lipids (GDGTs) were determined in surface sediments in Lake Sihailongwan Maar, in order to investigate the composition and sources of the organic matter. The results indicated that fatty acids were the main component of the dissolved organic matter in the sediments of the lake, accounting for 68.8% of TOC, which were mainly endogenous algae and bacteria. The aliphatic hydrocarbons were mainly from terrestrial sources, with C3 plants being major contributors. The bound alcohols were mainly from endogenous sources, while the free alcohols were mainly from terrigenous sources. The GDGTs, including branched GDGTs and isoprenoids GDGTs, were rich in the sediments of Lake Sihailongwan, and were mainly from the terrestrial soil. The isoprenoids GDGTs were dominated by GDGTs Ⅳ and Ⅴ, but their contents were limited in the surface sediments of the lake. The present study indicated that the organic matter from the watershed of Lake Sihailongwan was the major source in the surface sediments, while the influx of terrigenous organic matter was the main reason for the eutrophication level changes. The different kinds of dissolved organic matter showed different source characteristics, which was mainly attributed to the different degradation rates for microbes to different kinds of organic matter. In addition, the number of secondary organic matter from microbial degradation was also different.