The ability to regulate charge separation is pivotal for obtaining high efficiency of any photoelectrode used for solar fuel production. Vacancy engineering for metal oxide semiconductor photoelectrode is a major strategy but has faced a formidable challenge in bulk charge transport because of the elusive charge self‐trapping site. In this work, a new deep eutectic solvent to engineer bismuth vacancies (Bivac) of BiVO4 photoanode is reported; the novel Bivac can remarkably increase the charge diffusion coefficient by 5.8 times (from 1.82 × 10−7 to 1.06 × 10−6 cm2 s−1), which boosts the charge transport efficiency. Through further loading CoBi cocatalyst to enhance charge transfer efficiency, the photocurrent density of BiVO4 photoanode with optimal Bivac concentration reaches 4.5 mA cm−2 at 1.23 V vs reversible hydrogen electrode under AM 1.5 G illumination, which is higher than that of previously reported Ovac engineered BiVO4 photoanode where the BiVO4 photoanode is synthesized by a similar procedure. This work perfects a cation defect engineering that enables the potential capability to equate the charge transport properties in different types of semiconductor materials for solar fuel conversion.