The detritus input and removal treatments (DIRT), as an experimental design to study the effects of carbon input on soil texture and quality, plays a key role in the study of soil nutrient sources and main influencing mechanisms. In this study, the natural Castanopsis carlessii forest in the Sanming forest ecosystem and global change research station in Fujian province was selected, and five treatments were set up, including control (CT), no litter (NL), no roots (NR), no input (NI), double litter (DL), 0-10 and 10-20 cm soil samples in each treatment were collected in december 2018 to study the soil organic carbon fractions and their influencing factors. The results showed that:(1) In the 0-10 cm soil layer, the contents of NH₄⁺-N and total N (TN) in DL treatment were significantly higher than those in other treatments. The contents of NH₄⁺-N and dissolved organic N (DON) in NR treatment were significantly greater than those in NL and NI treatment. In the 10-20 cm soil layer, the contents of NH₄⁺-N, NO₃^--N, DON and TN in the DL treatment were significantly greater than those in other treatments. The contents of NH₄⁺-N in NI treatment was significantly lower than that in other treatments. (2) The contents of organic carbon in DL treatment was significantly higher than that in NL treatment, but there was no significant difference in soil organic carbon content between DL treatment and CT treatment (P>0.05), and there was no significant difference among other treatments. (3) The contents of active carbon fraction in the treatment with litter was significantly higher than that in the treatment without litter, and the order of active carbon fraction content was DL > CT > NR > NL > NI. The content of soil recalcitrant carbon in litter removal treatment (NL) was significantly higher than that in root removal treatments (NL and NI). (4) Litter and root input had significant effects on the activities of β-glucosidase and cellobiohydrolase in 0-10 cm soil layer, showing the same changing trend as soil active carbon. Redundancy analysis showed that the variation of soil organic carbon fractions was mainly controlled by β-glucosidase activity. The pH value and soil moisture content were also key factors affected soil organic carbon and its fractions. Litter input was conducive to improve the availability of soil nutrients and soil quality, and accelerate the carbon cycle, while plant roots played a key role in the stability of organic carbon in the soil.