Bismuth vanadate (BiVO4) has been one of the most promising candidates for solar water splitting while still suffers from poor bulk charge transport that limits its solar to hydrogen conversion efficiency.We demonstrate in this work an efficient strategy for boosting bulk charge transport of BiVO4 through the facile impregnation of as-prepared BiVO4 photoanode in the precursor solution of ultrathin BiOI nanosheets.Such impregnation creates increased oxygen vacancies in the bulk of BiVO4 through the reduction of V5+ to V4+ by I,which greatly improves bulk separation efficiency for BiVO4-BiOI up to 65.9％ at 1.23 VRHE from the original 51.9 ％ of pure BiVO4.Moreover,the decoration of the BiOI nanosheets on BiVO4 photoanode is also beneficial for addressing the carrier dynamics at surface due to the matched energy levels of BiOI nanosheets and BiVO4.The introduced plenty of oxygen vacancies in the bulk of BiVO4 and the built-in electric field in BiVO4-BiOI synergistically improve the photocurrent density at 1.23 VRHE up to 3.88 mA cm-2.We believe that such facile impregnation strategy will pave an alternative way to the development of highly efficient BiVO4 photoanode.