In order to investigate the effects of different carbon sources addition on soil dissolved organic matter (DOM) content and composition, a 360-day incubation experiment with UV-visible and fluorescence spectroscopy analysis was conducted. The treatments included control (CK), soil + 1% biochar (SB), soil + 1% leaf litter (SL) and soil + 1% fine roots (SR). The results showed that compared with CK, the SL and SR treatments significantly increased soil dissolved organic carbon (DOC) at 30, 90, and 180 d, while the SB treatment significantly decreased soil DOC content at 360 d. The SL and SR treatments significantly enhanced the aromaticity of soil DOM at 30, 180, and 360 d, whereas SB had no significant effect. The humification index (HIX) of DOM in SL, SR, and SB treatments was significantly higher than that in CK. Notably, the SL treatment promoted soil DOM humification more effectively than SR and SB. Fluorescence spectroscopy analysis identified three components of SOM: fulvic acid-like(C1), tyrosine-like(C2), and tryptophan-like(C3). With incubation time, C1 decreased and C2 increased in all treatments, while C3 remained relatively stable in SR and SL. Correlation analysis showed that, C1 was significantly positively correlated with soil total nitrogen content and significantly negatively correlated with C:N, C2 was significantly negatively correlated with soil NH₄⁺-N content, C3 was significantly positively correlated with soil NO₃^--N content and significantly negatively correlated with both the humification index (HIX) and total carbon content. In conclusion, the addition of leaf 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 provided a scientific basis for further understanding the dynamic changes of DOM in subtropical forest soils.