This review comprehensively summarized the progresses in the design and modification of titanium dioxide (TiO2) nanostructures as photoelectrode materials for photoelectrochemistry (PEC) applications, mainly in solar-fuel conversion. Various kinds of TiO2 nanostructures including the nanoparticulate, one-dimensional (nanowires, nanorods, nanotubes), two-dimensional (nanobelt, nanoribbon, nanosheet), three-dimensional (meso/nanoporous, branched nanostructures, etc.), and the crystal-facet tailored TiO2 nanostructures are surveyed and discussed. For each type of nanostructure, the commonly-used and effective modification strategies are reviewed followed with a deep discussion on the properties relevant to PEC performances. Moreover, the surface modification approaches (surface disordering, passivation and decoration) on TiO2 nanostructures are highlighted for developing efficient TiO2-based PEC cells. This review will serve as a good resource or guideline for researchers who are currently focusing on TiO2 materials as well as for those who are interested in versatile semiconductor-based PEC applications.