Abstract: TiO ₂ is one of the most popular photocatalysts that has been widely studied and applied, due to its advantages of non-toxic, low cost, good catalytic activity and stability. Although there are a large number of experimental research on photocatalytic water-splitting over TiO ₂, it is very necessary to investigate and understand the basic process of photocatalytic water-splitting from the micro scale. Based on the primary simulation methods of molecular dynamics, density functional theory, and first principles molecular dynamics, the latest developmemts on the photocatalytic water-splitting over TiO ₂are reviewed from three aspects: adsorption forms and layered structure of water on TiO ₂ surface, energy barrier and rate-determining step of the water-splitting reaction, and the charge transfer process in TiO ₂ surface. The exited problems of current research and the research emphasis in the future are also analyzed and discussed.