Suspended particulates and sediments are the main substances of lake organic pollutants and organic carbon, and their stable isotope research is of great significance for effectively identifying lake eutrophication. We select Lake Wuliangsuhai as our research site to measure and analyze the index, such as δ¹³C, C/N, total organic carbon (TOC, POC) and total nitrogen (TON, PON) content of organic matter in surface sediments and suspended particulates of the lake area and the inflow canal in April (melting period), July (summer irrigation period) and October (autumn irrigation period) in 2019. We used δ¹³C and C/N in combination with isotope multivariate mixed model to investigate the sources and contributions of the lake organic carbon. The results indicate that the variations of δ¹³C_POC in the suspended particulates organic carbon range from -23.29‰ to -29.75‰, with a trend of October>April>July and inflow canal>lake area. POC/PON ratio of the suspended particulates changes from 4.10 to 21.35, with a trend of October>July>April. The suspended particulate organic matter mainly comes from phytoplankton (51.59%), silt of the inflow canal (34.60%) and macrophyte (13.76%). The δ¹³C_TOC value of the bottom sediment organic carbon varies from -27.58‰ to -22.68‰, with a tendency of April72.79%), while the contribution rate of phytoplankton and macrophyte is relatively low (11.85% and 15.36%, respectively). This study estimates the sources of organic carbon in the suspended particulates and bottom sediments in a eutrophic lake affected by the inflow canal, and provides an in-depth understanding for improving the lake pollution and studying organic carbon sources.