The weak electron-hole pair separation and transfer of the BiVO4 photoanode restrain its photoelectrochemical performance of water splitting. In this work, we focus on Zn doping to replace Bi-sites within BiVO4 nanocrystals to promote efficient charge separation and transfer. Theoretical and experimental results show that Zn doping induces oxygen vacancies with controllable content. Zn doping and oxygen vacancies not only shift the conduction and valance band positions of BiVO4, resulting a local built-in electric field, but also increase the carrier density, which would be beneficial for charge separation and transfer. In the meantime, water adsorption on Bisites is also activated, which would help water splitting. As a result, these contributions synergistically enhance photoelectrochemical performance with the incident photon-to-current conversion efficiency (IPCE) of 34% at 0.6 V vs. RHE, which is much higher than that of pristine BiVO4. Furthermore, by sequentially electrodepositing graphene quantum dots (GQDs) and cobalt phosphate (Co-Pi) nano-film, we have constructed a hybrid ZnBiVO4/GQDs/Co-Pi structure to broaden the light absorption and to enhance the stability, its IPCE reaches as high as 57% and photocurrent density achieves 3.01 mA cm(-2) at 0.6 V vs. RHE, which is 8.6 times of the pristine BiVO4, thus providing an efficient strategy for the structure design of BiVO4 based photoelectrodes.