The TiO2 nanobelt/ZnO nanorod composite photoelectrodes with flower-like and/or grass-like microstructures have been fabricated via a facile solution growth routine, just by controlling the treatment of the TiO2 nanobelt substrate. For the flower-like composite, the ZnO nanorods disperse orientationally on TiO2 nanobelt films, while for the grass-like one, ZnO nanorods grow disorderly like grass on the TiO2 nanobelt film surface. Furthermore, quasi-Fermi energy level changes of both photoelectrodes have been quantitatively characterized by the surface photovoltage based on the Kelvin probe, which clearly reveals the efficiency of photogenerated electron-hole separation. Owing to the decrease of quasi-Fermi energy level, the flower-like TiO2 nanobelt/ZnO nanorod heterogeneous nanostructure presents a high efficiency of photogenerated electron-hole separation. Therefore, the flower-like TiO2 nanobelt/ZnO nanorod heterogeneous nanostructure photoelectrode has achieved a better performance of water splitting compared with the grass-like TiO2 nanobelt/ZnO nanorod one.