We demonstrate that moderate hydrogen annealing is a simple and effective approach to substantially improve the photocatalytic activity of TiO2 nanorods via increasing oxygen vacancies in outer layer. Hydrogenated TiO2 nanorods are obtained by annealing in hydrogen atmosphere at various temperatures ranging from 200 degrees C to 350 degrees C. TEM images directly illustrate the disordered layer on the surface of nanorods induced by hydrogen annealing. The photoelectrochemical measurements reveal that the photocurrent is improved first as the temperature increases and reaches to the maximum value at an appropriate temperature (250 degrees C), corresponding to about 50% enhancement compared to the pristine TiO2. Incident photon-to-electron conversion efficiency spectra reveal that the photocurrent improvement is mainly attributed to the enhanced photocatalytic activity of TiO2 in ultraviolet region. Mott-Schottky plots further betray that hydrogen annealing can significantly enhance the electric conductivity, via increasing the oxygen vacancies density in the outer layer. In addition, time-dependent measurements indicate the hydrogenated TiO2 nanorods possess excellent chemical stability. Thus, we believe the hydrogenated TiO2 nanorods would be a promising candidate for photoanode in solar water splitting.