Abstract: Dissolved organic matter is an essential effect on the conversion exchange between organic matter and inorganic matter in nature environment, which is widely distributed in water, soil and sediments. As a pollutants carrier, it affects the migration and transformation of contaminants, while it also provides carbon source and nutrients for microorganisms. For exploring the composition, source and humification degree of DOM in Moguhu Lake, the components of DOM in the overlying water was analyzed by using three-dimensional fluorescence spectroscopy combined with parallel factors. The source and humification degree were studied by means of spectral index (FI, HIX, BIX), and the correlation and relationship between FI and F_max were used to explain the type and characteristics of DOM. The results show that in Moguhu Lake, DOM of overlying water contains four components, which are two represent fulvic acid substances for C1 and C4, tryptophan in the protein C2 and humic acid C4. Secondly, the DOM is mainly composed from microbial endogenous metabolites with high bioavailability and low degree of humification. Positive correlation was found between each component F_max and FI, and a significant positive correlation existed between fulvic acid and FI. According to previous studies, in Moguhu Lake, the primary component of DOM is fulvic acid-like substance, which contains a reactive functional group such as a carbonyl group or a hydroxyl group with small molecular, and with characteristics of a low degree of humification, aromaticity, and low molecular condensation.