Perovskite BaTaO2N (BTON) is one of the most promising photocatalysts for solar water splitting due to its wide visible-light absorption and suitable conduction/valence bands,but it still confronts the chal-lenge of high defect density causing decreased charge separation as well as photocatalytic activity.In this work,we develop a simple zinc doping strategy to greatly suppress its defect density and promote its water reduction performance.It is found that the defect formation on the nitrided Ba(Zn1/3-xTa2/3)O3-yNz (denoted as BZTON hereafter) will be greatly inhibited when the Zn-doped Ba(Zn1/3Ta2/3)O3(BZTO) oxide is used as the nitridation precursor.The structural characterizations and discussion demon-strate that the effective inhibition of Ta5+ into Ta4+ defects in BZTON mainly results from the easy reduc-tion of zinc ions into metal and further the evaporation of zinc metal under the thermal ammonia flow.Interestingly,this simply doping methodology can be easily extended into the synthesis of SrTaO2N(STON) with extremely low defect density,demonstrating its generality.Benefiting from the successful control to the defect density,the as-obtained BZTON photocatalyst exhibits remarkably promoted charge separation as well as water reduction activity to produce hydrogen with respect to the pristine BTON.Our work may provide an alternative avenue to prepare oxynitride semiconductors with reduced defect den-sity for promoted solar energy conversion.