Defect engineering is recognized as an effective route to obtaining highly active photocatalytic materials. However, the current understanding of the role of defects in photocatalysts mainly comes from their independent functional analysis, ignoring the synergy between defects and the chemical environment, especially with crystal facets. Herein, oxygen vacancy (VO)-rich TiO2 nanostructures with different dominant exposed facets were prepared, and the microstructural changes induced by the synergy between the VO and facet effect and the performance difference of photocatalytic O2 activation were explored. The results showed that the combination of high concentration VO and the {101} facet is more conducive to improving the photocatalytic performance of TiO2, which is significantly superior to the combination of low concentration VO and the {101} facet as well as the combination of high concentration VO and the {001} facet. The experimental and theoretical results clarified the dependence of each stage of photocatalysis on two factors. Specifically, VO plays a more significant role in energy band regulation, improving the dynamic behavior of photogenerated charges and enhancing the adsorption and activation of O2, while the facet effect made more contributions to reducing the thermodynamic energy barrier of ROS formation and conversion. The excellent ability of O2 activation enables T101-VO to show potential application characteristics in the removal of RhB and bacterial disinfection. This work established a link between defect and facet effects, providing new insights into understanding defect function in photocatalysts.