The choice of support is one of the most significant components in the direct synthesis of H2O2. Aiming to improvement of activity and selectivity of H2O2 on Pd/TiO2 surface, we systematically investigated the important elementary steps on Pd/TiO2-Vo@C, Pd/TiO2-Vo, Pd/TiO2-2Vo, Pd/TiO2, and Pd/C using the first-principles calculations. The Bader charge analysis and charge density difference of O2 adsorption elucidate the relationship between the electronic distribution and chemisorption energy. The effective barrier analysis further enables to quantitatively estimate the reactivity of H2O2 and H2O. We demon-strate unambiguously that the selectivity of H2O formation is boosted as the oxygen vacancy concentra-tion raised. Moreover, the introduction of C into a TiO2 with appropriate oxygen vacancies can slightly reduce the effective barrier for H2O2 formation and increase the effective barrier for H2O formation lead-ing to a higher activity and selectivity of H2O2 formation. Our finding suggests that carbon-doped oxygen vacancy TiO2 supported Pd is potential alternative catalyst compared with the Pd/TiO2.