To explore characteristics of δ ¹³C value of soil organic carbon (SOC δ ¹³C) under naturally restoring degenerative forest in the karst region of Maolan, the technique of stable carbon isotopes coupled with the concept of space substituting time was adopted. Results show that as a whole, SOCδ ¹³C in the 0~20 cm soil layer(-25.72‰~-19.91‰) increased along with the restoration in process, turning gradually towards positive, but SOCδ ¹³C in soil layers >20 cm (-23.76‰~-18.13‰)in depth turned towards positive at early stages and then backwards at later stages; SOC δ ¹³C turned towards positive increased with soil depth at all stages except at the grass-shrub and shrub-arbor stages; SOC in the upper soil layer at the grass-stage and in the lower soil layer at the arbor and climax stages was dominated with C₄; SOC δ ¹³C were jointly affected by zonality and karst environment; δ ¹³C in litters of dominant species (-31.79‰~-16.76‰)turned towards negative along with the restoring process, indicating that the habitat was improving, and besides, it was significantly and positively related to SOCδ ¹³C in the 0~20 cm soil layer（R²>0.96，p<0.01）, but negatively to that in the soil layers >20 cm in depth, indicating that the carbon in the upper layer was new; the turn-over rate of SOC increased with the restoring process, but decreased with soil depth; soil biochemical reaction occurred mainly on the surface of the soil; SOC δ¹³C exhibited significant negative relationships with contents of mineralizable carbon and readily oxidizable carbon (R²>-0.50, p<0.05), and certain negative relationship with microbial biomass carbon(R²=-0.389), indicating that SOC δ¹³C can, to a certain extent, be used as indicator of SOC activity; natural restoration of karst forest vegetation was a complicated and variable integration of multi ways, among which C4 plants played a role of important significance in process of natural restoration. The stable carbon isotope technique coupled with the concept of “space substituting time” can be used to rehearse the history of vegetation succession in karst regions.