Urban polluted landscape water was purified by macrophytes that absorb nutrients and degrade pollutants. However, macrophytes are decomposed in autumn and winter, affecting water quality since they release the absorbed nutrients and pollutants back into the environment. Meanwhile, dissolved organic matter (DOM) released by decomposing macrophytes sharply increases organic pollutants. Previous studies focused on the macrophyte-purified water, biodiversity maintenance of landscape water, and eco-culture lineage, but just a few of them studied the negative effects of urban polluted landscape water purified by macrophytes. DOM is a complex mixture of compounds, most of which remain unknown, because it is hard to separate and characterize them. These compounds affect the distribution of pollutants, such as heavy metals and organic pollutants that react with DOM to form an even more complex mixture. Lake Baiyangdian is one of the largest lakes in north China that serves as an aquaculture and aquatic natural reserve, and contributes to the adjustment of the surrounding climate and carbon cycling. In this study, we investigated the effect of DOM released by macrophyte decomposition during the winter in Lake Baiyangdian, where mounts of phytoplankton, emergent aquatic plants, and submerged plants are grown. We used UV-vis and fluorescence spectra combined with Parallel Factor (PARAFAC) and Principal Component Analysis (PCA) to study DOM released by macrophyte decomposition and reveal its humification degree, aromatic degree, and molecular weight. UV-vis results indicated that the number of plants positively affected the number of carboxyl, carbonyl, and esters groups in DOM molecular composition. The humification degree increased with increasing decomposition time, but it decreased after reaching the peak value, probably because decomposition process entered into the mineralization phase. PARAFAC provided more detailed information on the components in DOM samples that hardly detected by traditional peak picking. Five components were identified by PARAFAC, including 3 protein-like components (C1, C2, and C5) and 2 humic-like acid components (C3 and C4). C1 was classified as tyrosine-like group, C2 and C5 were classified as tryptophan-like groups, C4 was dominated by humic-like acid, and C3 was a combination of marine and terrestrial humic-like acids. Correlation analysis showed that C3 was significant positive correlated with C4, as well as C1, C2 with C5, results that indicated the close relationship of protein-like substances with humic-like acids. PCA provided information on the contribution of components in DOM samples. The results showed a relatively high factor 1 score in the beginning of decomposition, indicating that the protein-like substances were dominant. During the process of decomposition, the proportion of protein-like substances decreased and the humic-like substances increased. At the end of decomposition, the humic-like acids had a relative high proportion and were dominant in DOM samples