In order to investigate the characteristics, sources and variations in the composition of chromophoric dissolved organic matter (CDOM) during the normal and rainy seasons in the reservoir of the Yellow River Diversion Source Reservoir-Menlou Reservoir, UV-vis and EEMs techniques combined with PARAFAC were used to analyse the changes in CDOM content and components in May 2022 (normal season) and July 2022 (rainy season). The results of the study showed that PARAFAC identified 2 types of fluorescent fractions, C1 (Ex=355 nm, Em=476 nm, humus-like fraction) and C2 (Ex=225 nm, Em=320 nm, protein-like fraction). The fluorescence intensity of the CDOM fraction was significantly higher in wet seasons than in normal seasons. The spectral parameters of CDOM indicated that the water body of Menlou Reservoir was in a mesotrophic state, and the CDOM of the water body was mainly autogenous due to the combined effects of endogenous and exogenous inputs. The reservoir CDOM was characterized by low relative molecular weight and low humification. The levels of eutrophication and the relative concentrations of CDOM in the reservoir were lower in the wet season than in the normal season, and the proportion of hydrophobic components and the degree of aromatization of CDOM were higher than in the normal season. Correlation analysis of water physical and chemical indicators, CDOM components and spectral parameters showed that SUVA₂₆₀ and SUVA₂₈₀ were significantly negatively correlated with DOC, indicating that UV-Vis spectral parameters could be used to estimate the concentration of DOC to some extent; Chl.a concentration, as an indicator characterizing phytoplankton biomass, was significantly and positively correlated with DOC, a₂₅₄. The study revealed the fluorescence characteristics, component source response mechanism and water period variation of CDOM in the water body of Menlou Reservoir, providing basic data for further investigation of the environmental behavior characteristics of CDOM in the Yellow River Diversion Water Source Reservoir, its contribution to water eutrophication and its influence on the environmental behavior of other pollutants.