As an active component of the soil carbon pool, soil dissolved organic matter (DOM) plays an important role in the carbon cycle. This study investigated the effects of different carbon sources addition on soil DOM content and composition using a 360-day incubation experiment with UV-visible and fluorescence spectroscopy analysis. The experiment treatments included the CK (soil), SB (soil + 1% biochar), SL (soil + 1% litter) and SR (soil + 1% fine root). The results showed that compared with the CK, the SL and SR treatments significantly increased soil dissolved organic carbon (DOC) content at 30, 90, and 180 days, while the SB treatment had significantly decreased soil DOC content at 360 days. The aromaticity index (SUVA254) showed a trend of rapid increase followed by a gradual decrease. The SL and SR treatments significantly enhanced the aromaticity of DOM at 30, 180, and 360 days, whereas the SB treatment had no significant effect. The humification index (HIX) of the SL, SR, and SB treatments were significantly higher than that of CK treatment. Notably, the SL treatment promoted soil DOM humification more effectively than the SR and SB treatments. Fluorescence spectroscopy analysis identified three components: fulvic acid-like(C1), tyrosine-like(C2), and tryptophan-like(C3). In all treatments, the C1 component decreased with incubation time, while the C2 component increased. The C3 component remained relatively stable in the SR and SL treatments. Correlation analysis showed that the C1 component was significantly positively correlated with soil total nitrogen (TN) and significantly negatively correlated with soil C:N. The C2 component was significantly negatively correlated with soil ammonium nitrogen (NH4?-N). The C3 component was significantly positively correlated with soil nitrate nitrogen (NO3--N) and significantly negatively correlated with both the humification index (HIX) and total carbon (TC). Collectively, the addition of litter and fine roots significantly enhanced the aromaticity and humification of soil DOM compared to biochar addition, and promoted the accumulation of microbially-derived components in soil DOM. This study provides a scientific basis for further understanding the dynamic changes of DOM in subtropical forest soils.