Abstract: Dali-Nor Lake (referred to as 'Dali Lake') is an important ecological barrier in the plateau of Inner Mongolia. It is of great significance to explore the current situation of water quality and analyze the pollution sources of Dali Lake for strengthening the basin management of the water environment and improve the quality of the water environment. Lake samples were collected in September 2018 and June 2019, and analyzed using the three-dimensional fluorescence spectra-parallel factor analysis (PARAFAC) to investigate the source of DOM and its relationship with water quality. The results showed that: (1) The pH of Dali Lake was relatively high, and the average concentrations of nutrients including ρ(DOC), ρ(NH₄⁺-N) and ρ(TP) were also relatively high, all exceeding Surface Water Environmental Quality Standard (GB 3838-2002) Class V water quality standard limit. (2) A total of 4 fluorescent components were observed in DOM. In summer, DOM is mainly distributed near the river mouth, humic-like fluorescent components (ultraviolet-like fulvic acid and visible-range fulvic acid) accounted for 62.93% of the total fluorescent components, while protein-like fluorescent components (tryptophan and tyrosine) accounted for 36.07%. In autumn, DOM mainly distributed on the southeast side, humus-like fluorescent components accounted for 40.52%, and protein-like fluorescent components accounted for 59.48%. (3) Across all the sampling sites, the fluorescence parameters indicated that the bio-source characteristics of DOM from Dali Lake were strong whereas the humification degree was low. The humic-like fluorescent component had a positive correlation with ρ(DOC) and ρ(Chla), the tryptophan-like fluorescent component had a positive correlation with pH, and the tyrosine-like component had a positive relationship with ρ(DTN), ρ(NH₄⁺-N) and ρ(DTP). This study shows that the DOM of Dali Lake has dual characteristics of terrestrial and biological sources, and the formation of DOM is closely related to the life activities of microorganisms, bacteria, and plankton.