The interaction between several different metal ions and H2O along with CO2 has been researched theoretically in the CO2 photocatalytic reduction with H2O system at the B3LYPlevel by DFT. The computational results revealed that relatively high valence metal ions loaded on TiO2 activated the H2O and CO2 consumingly, and it might be looked as some proofs for modified photocatalyst selecting. In addition, the metal ions conducted photoelectrons to prevent the recombination of photoelectrons and holes during the reaction process.