The hydrogen sulfide (H2S) removal ability of activated carbon is closely related to surface oxygen groups, yet the roles of oxygen groups in the process of H2S adsorption on activated carbon have heretofore been unclear. The interactions of H2S with various oxygen groups on activated carbon were detailed examined by density functional theory. The results indicate that pyrone, carbonyl, ester, and carboxyl groups are active sites for H2S adsorption, except for hydroxyl group. H2S can react directly with carbonyl oxygen atom in these oxygen groups leading to the formation of C-S, C-OH, and C-SH species. A pyrone group can improve the activity of surface carbon sites for H2S adsorption. The presence of non-neighboring epoxy oxygen atom increase evidently the activity of carbonyl oxygen atom for H2S adsorption. The relative position of the carbonyl oxygen atom and epoxy oxygen atom plays a key role in the activity of oxygen groups.