It is very important to explore a cheap but efficient catalyst as a counter electrode in a dye-sensitized solar cell (DSSC). In the present work, density functional theory (DFT) calculations were performed to investigate the reduction of triiodide ion catalyzed by a metal atom embedded in graphene. It is shown that the binding energy of a single Pt atom embedded into the divacancy of graphene (Pt@DV) is about -11.0 eV, larger than the location of Pt at single vacancy (Pt@SV). In the Pt@DV with a Pt loading of 25 wt %, the adsorption energy of the iodine atom and the dissociation energy of the iodine anion are respectively -1.54 and 0.60 eV, indicating a potential high catalytic activity of Ptgraphene. Further investigations of diverse transition-metal-embedded graphenes ranging from Sc to Zn imply that the Co-embedded graphene (in divacancy) may be a good candidate to be utilized as counter electrode in DSSC.