Abstract: The composition, temporal and spatial distribution and source characteristics of humus in the Heilongjiang River Basin were studied via field investigations, static immersion and leaching dynamic experiments. Fluorescence characteristics and sources of dissolved organic matter (DOM) in typical Heilongjiang River Basin were analyzed by EEM-PARAFAC. The results showed that: (1) The concentration of COD_Mn was abnormally high during the normal and wet seasons. The relative content of DOM was much higher than that during the dry season. Four fluorescence components, including UVA humic-like substances (C1), UVC humic-like substances (C2), marine humic-like substances (C3) and tryptophan-like substances (C4) were detected in a typical Heilongjiang River Basin. Among them, the total contribution of humic-like substances accounted for over 50%. Therefore, humic-like substances were the most important factors affecting DOM in the Heilongjiang River Basin. The fluorescence index (FI) values of DOM during the normal, wet and dry seasons were 1.48-1.61, 1.51-1.63 and 1.52-1.79, respectively. The biological source index (BIX) values of DOM during the normal, wet and dry seasons were 0.56-0.75, 0.55-0.73 and 0.61-0.92, respectively, and the humification index (HIX) values of DOM were 5.84-13.42, 5.70-15.78 and 2.84-12.05, respectively, indicating that DOM mainly came from land sources and autogenous sources with autogenous source characteristics and significant humus characteristics. (2) Static immersion and dynamic leaching experiments were carried out to simulate soil dissolution and rainfall process. Consequently, five fluorescence components were detected during leaching process. In addition to C1-C4, tyrosine-like substances (C5) were found. Due to similar fluorescence characteristics of DOM in soil and water, it is concluded that the DOM in water and soil had similar sources in the Heilongjiang River Basin. (3) A linear correlation between fluorescence component intensity and DOC concentration during the normal, wet and dry seasons was observed. Humic-like substances and marine humic-like substances had significant linear correlation with DOC concentration. The correlation coefficients of C1, C2 and C3 during the normal, wet and dry seasons were 0.7762, 0.8524 and 0.9568, 0.4783, 0.2659 and 0.8784, 0.6582, 0.8025 and 0.9545, respectively. In comparison, there was a large gap between the correlation coefficient between C4 and DOC concentration. The correlation coefficients of C4 during the normal, wet and dry seasons were -0.0644, 0.0219 and 0.8474, respectively, indicating that the humic-like fluorescence components were the main sources of DOC in the Heilongjiang River Basin. In summary, the humic-like components were the main components of water DOM in the Heilongjiang River Basin. The water body had obvious DOM characteristics, and the background value of source water was relatively high.