Nitrogen-doped oxides are one kind of photocatalysts with wide spectrum absorption for promising solar water splitting, but they usually exhibit poor charge separation and thermal instability in air, leading to challenging construction of overall water splitting (OWS) system. Here we adopt one-pot nitridation strategy to synthesize a series of heterostructured photocatalysts based on Ta3N5 and the newly reported nitrogen-doped oxide BaMg1/3Ta2/3O3-xNy (denoted as BMTON) with absorption wavelength of 560 nm. The as-obtained typical heterostructure BaMg1/3Ta2/3O3-xNy/Ta3N5 (denoted as BMTON/Ta3N5) is found to exhibit superior charge separation and transfer ability with respect to the corresponding counterparts, as has been ascribed to their well-matched band gap structure and intimate interface contact. As a result, the photocatalytic activity of proton reduction over the optimized heterostructure BMTON/Ta3N5 (0.4) is about 20 times higher than that of the counterparts, based on which effective Z-scheme OWS system under visible light irradiation can be realized by using the heterostructure BMTON/Ta3N5 as H-2-evolving photocatalyst. This work not only gives a further proof that one-pot nitridation is a general strategy to fabricate heterostructure composed of nitrogen-doped complex oxide for enhanced charge separation and photocatalytic performance, but also demonstrates the promising future of nitrogen-doped oxide in constructing artificial photosynthesis devices.