Abstract: To elucidate the regulatory effects and mechanisms of carbon source addition on the migration of soil dissolved organic carbon (DOC) in purple soil areas of hilly regions in central Sichuan under heavy rainfall conditions, this study aimed to provide a scientific basis for the effective control of carbon loss in sloping farmland.Taking purple soil sloping farmland as the research object, the study employed a combination of field runoff plots and laboratory analysis.Using chemical fertilizer alone (CK) as the control, six carbon source addition treatments were established: organic fertilizer (T1), compound microbial fertilizer (T2), biochar-cattle manure-mushroom residue compost (T3), corn straw biochar (T4), upgraded organic fertilizer (T5), and organic soil amendment matrix (T6).This study investigated the changes in soil dissolved organic carbon content and spectroscopic characteristics at different slope positions.The results showed that exogenous carbon addition significantly increased the DOC content at different slope positions.The DOC content at the upper slope position increased by 51.53%–61.34% compared to the control group, with the organic fertilizer treatment showing the most significant enhancement effect.At the middle slope position, the DOC content increased by 16.73%–65.86%, with the biochar-cattle manure-mushroom residue compost and upgraded organic fertilizer treatments significantly increasing by 65.86% and 61.81%, respectively, compared to CK.These treatments also exhibited a significant delaying effect on DOC migration to the lower slope.No significant differences in DOC content were observed among treatments at the lower slope position.The degree of DOC aromatization exhibited significant spatial heterogeneity: the biochar-cattle manure-mushroom residue compost treatment increased the DOC aromatization degree by 12.63% at the upper slope position, while the corn straw biochar and organic soil amendment matrix treatments significantly reduced by 10.10% and 16.93%, respectively.At the middle slope position, the DOC aromatization degree generally showed a decreasing trend.At the lower slope position, the biochar-cattle manure-mushroom residue compost treatment demonstrated the best enhancement effect, significantly increasing the DOC aromatization degree compared to the control.The proportions of DOC components were as follows: soluble microbial byproduct-like > humic acid-like > fulvic acid-like > tryptophan-like > tyrosine-like.The humic substances primarily originated from endogenous microbial decomposition processes.The corn straw biochar and biochar-cattle manure-mushroom residue compost treatments significantly increased the humification index by 56.93% and 71.84%, respectively.The application of biochar-cattle manure-mushroom residue compost not only effectively enhanced soil DOC content and aromatization degree, but also significantly delayed its migration along the slope, promoting DOC enrichment at the middle slope position.This approach achieved multiple benefits, including improved soil fertility, delayed carbon migration, and reduced potential pollution risks.