In order to investigate the fluorescence spectral characteristics, sources, and contributions of DOM (dissolved organic matter) in the Qiqihar Section of the main stream of the Nenjiang River, the fluorescence component characteristics of water DOM were qualitatively analyzed using 3D-EEM (three-dimensional fluorescence)-PARAFAC algorithm technology. The chemical properties, sources, and contributions of each fluorescent component of water DOM were quantitatively studied by combining fluorescence index and PCA (principal component analysis). The results show that there are two main organic components of DOM in Qiqihar Section of Nenjiang River, which are fulvic acid like component C1 and tryptophan like component, and the average fluorescence intensity of C1 account for 82.0%. The results of fluorescence index show that the water has strong humification characteristics, and the average value of HIX (humification index) is 0.82. Principal component analysis show that the source of DOM is a mixture of endogenous and terrestrial sources, with PC1 contributing 48.1% and PC2 contributing 36.5%. It is concluded that the land-based sources such as soil humus and agricultural non-point sources are the main sources of DOM in the Nenjiang River Mainstream in Qiqihar, and the endogenous sources such as aquatic organisms and microbial metabolic activities are the secondary sources.