Here SrTaO2N has been found to exhibit photoelectrochemical water splitting, with a theoretical solar-to-hydrogen efficiency of 14.4%. Ameliorating the interparticle charge transport by H-2 annealing, the solar photocurrent of the SrTaO2N(H) granular film at 1.23 V versus reversible hydrogen electrode (RHE) is increased by approximate to 250% in comparison with the SrTaO2N film. Using an aberration corrected scanning transmission electron microscope and super-X energy dispersive spectroscopy, the atomic scale observation has proved a decrease of oxygen concentrations in the surface of SrTaO2N(H) particle, which may allow its electrical conductivity to be increased from 0.77 x 10(-6) to 2.65 x 10(-6) S cm(-1) and therefore the charge separation efficiency has been greatly increased by approximate to 330%. After being modified by Co-Pi water oxidation catalyst, the SrTaO2N(H) photoanode shows a solar photocurrent of 1.1 mA cm(-2) and an incident photo-to-current efficiency value of approximate to 20% at 400-460 nm and 1.23 V versus RHE, which suggests that it is a new promising photoanode material for solar water splitting.