During photoelectrochemical water oxidation reaction process, excessive surface oxygen vacancies always trap the photogenerated holes and the surface recombination will be aggravated. We developed an ozone treatment method that could effectively heal surface oxygen vacancies and suppress the recombination of electron-hole pairs on the surface of two-dimensional WO3 nanoflakes. The ozone treatment method can oxidize the W5+ on the surface of photoanodes to decrease the surface oxygen vacancies, which results in a significant cathodic shift of onset potential in comparison with the pristine WO3 photoanode. Meanwhile, the bulk oxygen vacancies formed upon hydrogen treatment could be retained to increase the bulk conductivity for WO3.