Dissolved organic matter (DOM) plays an important role in transforming organic matter into inorganic matter in the natural ecosystem. DOM can provide nutrition and energy for microorganisms and has an important role in indicating the transfer and transformation of humus. Cow dung can improve the humification efficiency of corn straw, which makes better use of agricultural waste. In order to study the characteristics of DOM in the fermentation process of corn straw-cow dung, which were treated with 2:8 (T1), 4:6 (T2), 6:4 (T3) and 8:2 (T4), we adopted three dimensional fluorescence spectrum - parallel factor analysis method to analyze the fluorescence components of DOM in the fermentation substrate. Fluorescence index (FI) and biological index (BIX) were used to analyze the source of DOM; humification index (HIX) was used to characterize the humification degree of fermentation, and the correlation among the maximum fluorescence intensity of DOM components was analyzed. The results showed that the sources of DOM were influenced by both autochthonous and allochthonous sources (FI>1.4, 0.8fulvic-like acid>humic-like acid. There was a significant positive correlation between fulvic-like acid and humic-like acid. Based on these, according to the DOM fluorescence spectroscopy characteristics, to improve the utilization rate of straw in the fermentation process, the ratio of straw and cow dung is 6:4, which can be used as the reference value of actual composting.