Dissolved organic matter (DOM) is an active organic component in soil, and its source and composition can indicate the degree of soil humification and its relationship with the external environment. In this study, in order to scientifically monitor and evaluate wetland soil environmental quality, we collected the surface (0～20 cm) soil under different vegetation types of the Nianzishan Yalu River National Wetland Park in Heilongjiang Province, and applied three-dimensional fluorescence spectroscopy-parallel factor analysis method to measure the DOM fluorescence spectrum, and further analyzed the effects of soil physicochemical indexes on DOM composition. The results showed that the soil DOM humification index was between 2.562 and 9.052 under five vegetation types (including nine formations). The soil humification degrees of the deciduous broad-leaved forest and the deciduous broad-leaved shrub were higher than that of the meadow, followed by the marsh, and the soil humification degrees of the aquatic vegetation were the lowest. The fluorescence index was between 1.407 and 1.586. The soil DOM source had both exogenous and autogenic characteristics. The deciduous broad-leaved forest and the Phragmites australis (Cav.) Trin. ex Steud. marsh had obvious exogenous characteristics, but the aquatic vegetation and the Echinochloa crus-galli (L.) P. Beauv. Marsh had obvious autogenic characteristics. The biological index ranged from 0.482 to 0.662, and the contribution rate of recent autogenic characteristicwas low. Three types of five kinds of organic components were identified fromthe soil DOM. Humus-like substance (ultraviolet fulvic-like acid componentand visible fulvic-like acid component) had the largest relative proportion, and the soil samples with obvious exogenous characteristics had high content. Followed by protein-like substance (tyrosine-like componentand tryptophan-likecomponent), its content was higher in the soil sample with strong autogenic characteristics. Humic-like acid substance (humic acid component) was the lowest, and mostly existed in the xerophyte-mesophyte environment. Soil moisture content, pH value, and total organic carbon content had significant or significant effects on DOM composition. The three physicochemical indexes were positively correlated with the protein-like substance content and negatively correlated with the humus-like substance content. The correlation of moisture content, total organic carbon content with humic-like acid substancecontent were negative, respectively. Overall, in this wetland park, the soil samples of deciduous broad-leaved forest and shrubs are weakly acidic, with low moisture content and total organic carbon content, high degree of humification, obvious exogenous characteristic, high humus-like substance and humic-like acid substance content. However, under aquatic vegetation, the soil is nearly neutral, with high water content and total organic carbon content, a low degree of humification, obvious autogenic characteristic, and high protein-like substance content. The results of this study can provide basic data for the monitoring and evaluating soil environmental quality in permanent river wetlands in the cold northern region represented by this wetland park.