In this study, first principles calculations based on density functional theory (DFT) were used to accurately quantify the equilibrium Cd isotope fractionations produced during the formation of organic surface complexes (OSCs) and metal-organic frameworks (MOFs). The results showed that the equilibrium Cd isotope fractionations between OSCs and the aqueous solution at 25 ℃ were small and insensitive, i.e., Δ^114/110Cd_OSCs-aq=-0.34‰ to 0.02‰. In contrast, the formation of MOFs produced significant Cd isotope fractionations, i.e., Δ^114/110Cd_MOFs-aq=-1.92‰ to-0.29‰. Additionally, the more N and S atoms appear in the first coordination layer of Cd, the greater the equilibrium fractionation of Cd isotopes between MOFs and aqueous solutions. Our calculation results cover the experimental determination of Cd isotope fractionation in surface soil, indicating that the different occurrence states of Cd in soil organic matter control its isotopic composition. Finally, these fractionation data enrich the Cd isotope database, making it easier for scholars to quantitatively use Cd isotope methods to limit the migration and transformation process of Cd.