The Sr2FeTaO6/NaTaO3 heterojunction with the controllable molar ratio and space of heterojunction transitional zone were fabricated using in situ hydrothermal method by adjusting hydrothermal temperature and time. Comparing with the pure NaTaO3 nanosheets and Sr2FeTaO6 nanoparticles, the Sr2FeTaO6/NaTaO3 heterojunctions exhibit higher photocatalytic performances, due to introducing narrow-bandgap Sr2FeTaO6 component, which could obviously enhance its absorbability in visible light region and separation efficiency of photogenerated electron-hole pairs. Under visible light irradiation, the optimal Sr2FeTaO6/NaTaO3 heterojunction, with the molar ratio of 0.53 and space of heterojunction transitional zone of 0.35 nm, shows the best photocatalytic activity with the NO removal ratio of 72% in 40 min, hydrogen evolution rate of 1334 mu mol h(-1) g(-1) in 5 h, and apparent quantum efficiency (AQE) for hydrogen evolution of 38.8% at 420 nm. More interestingly, the space of heterojunction transitional zone, related to the interface bonding degree of heterojunction material, may not be the only factor which influences transferring and separating efficiency of photo-generated charge carriers, but it is certainly an important one, which provides a new cognitive perspective for constructing and understanding efficient heterostructure photocatalyst.