Dissolved organic matter (DOM) is a critical active carbon reservoir within aquatic ecosystems,influencing global carbon cycling,water quality regulation,and the dynamics of aquatic food webs significantly. The component and source of DOM in different water bodies significantly influence adsorption capabilities of environmental pollutants. Understanding the component and source of DOM in surface water is crucial for enhancing water quality. Rivers and smaller water bodies are important parts in watershed's surface water,and these water bodies exhibit substantial differences in flow velocity,water retention time,and microbial activity. Thus,this study collected water samples from primary and major secondary channels,minor secondary channels,and small water bodies across various hydrological periods-dry,normal,and flood-within a subtropical hilly watershed. Three-dimensional fluorescence spectroscopy and parallel factor analysis were used to clarify the variations in DOM component and source in the watershed's surface water. The findings revealed the following: (1) Dissolved organic carbon (DOC) concentrations adhered to the sequence of dry period > normal period > flood period,and small water bodies > main and large secondary channels > minor secondary channels. (2) The DOM in the watershed's surface water was comprised of two humic-like components (C1 and C2) and a single protein-like component (C3). Temporally,the percentage of C1 or C2 was highest during the normal period,followed by flood and dry period. However,C3 proportion was highest in the dry period,followed by flood and normal period. Spatially,the proportions of C1 and C2 were higher in main and large secondary channels,minor secondary channels,whereas C3 was highest in small water bodies. (3) The fluorescence index (FI) was significantly higher during the dry period,indicating increased autochthonous material input. However,the biological index (BIX) was lower in main and large secondary channels and minor secondary channels,reflecting greater terrestrial material inputs. We further analyzed the relationship between DOM components and water quality. Both of C1 and C2 had significantly positive correlations with permanganate index (COD_Mn). However,C1 or C2 showed no significant correlation with nitrate nitrogen (NO₃^--N),ammonium nitrogen (NH⁺₄-N),total nitrogen (TN) and total phosphorus (TP). C3 had a significantly positive correlation with NH⁺₄-N,TN,TP and COD_Mn,suggesting that the increase of protein-like component C3 was accompanied by the production of these nutrients. This indicates that the autogenous DOM may be an important source of nitrogen and phosphorus in the watershed's surface water. These findings provide scientific basis for protecting aquatic environments within the watershed.