Ex-service SF6 adsorbents in SF6 gas-insulated electric equipment contain many toxic substances. Inside, HF and H2S are two typical toxic gases. Based on the first principle, the interaction process between HF/H2S and α-Al2O3 (0001) surfaces was calculated using the density functional theory (DFT). The results showed that the adsorption of HF on α-Al2O3 (0001) is stronger than that of H2S. Under the five adsorption sites, the adsorption effect of HF-H and HF-F was similar. At O-2 site, the adsorption energy of H2S-H adsorption configuration is significantly higher than that of the other four sites. The density of states (DOS) indicated that new peaks appeared after adsorption. The DOS and partial density of states (PDOS) indicated that the adsorption of HF and H2S occurs via chemical adsorption. The DOS and PDOS shifted to the right when the S atom was approaching, proving that the system shifts to instability. Compared with the energy gap of α-Al2O3 (0001), HF and H2S adsorption systems decreased significantly. The energy gap of the HF adsorption system was 1.173 eV larger than that of the H2S system and the geometry was relatively stable, which is consistent with the DOS and PDOS adsorption calculation results. Thus, the adsorption of HF and H2S on α-Al2O3 (0001) surfaces was clearly different. The findings of this study may provide theoretical guidance for the adsorption of other gases or developing a new adsorbent.