The variation of dodecyl dimethyl betaine (DDB) on the surface properties of γ-dicalcium silicate (γ-C2S) was investigated through experimental and density functional theory approaches. The study also investigated the influence of DDB content on carbonation reactivity, carbonation products, and carbonation hardening characteristics. The results demonstrate that DDB can elevate the carbonation temperature of γ-C2S and enhance the dissolution of calcium ions, thereby promoting its carbonation activity. The appropriate content of DDB can enhance the dense aggregation of calcite on the surface of uncarbonated γ-C2S, thereby contributing to the densification and strength development of the matrix. DDB decreases the surface energy of γ-C2S and enhances its surface activity. Moreover, the (010) surface exhibits the lowest surface energy, facilitating the occurrence of robust chemical interactions and carbonation reactions. The enhancement mechanism of the carbonation reaction is associated with the interaction between carbonyl oxygen in DDB and surface calcium. There is a complexation between the two, which promotes the reaction with CO2. The results of this study possess significant implications for the selection of additives employed in modifying the surface properties of calcium silicate minerals and facilitating carbonation reactions.