The aim of this paper was to arise more attention to accelerating the separation and migration of photoexcited holes in the enhanced photocatalytic performances of composites. The highly effective h-BN/g-C3N4 was fabricated via an economical and environment-protecting way. Different characterization techniques were utilized to examine the crystal structure, morphology, interface, optical property and specific surface of photocatalysts. Their photosensitivity properties, resistance for charge migration and flat-band potentials were explored by the photoelectrochemical analysis. Remarkably, a substantially larger visible-light catalytic CO2 reduction of these composites was observed in contrast to pristine g-C3N4. The composite had the optimum BN dosage of 1 wt% and possessed good stability. The best kinetic constant of RhB degradation was 7.3 times that of bulk g-C3N4. Plate-like negatively charged BN as an efficient transfer of photoinduced holes were primarily responsible for the highly effective carriers separation in these prepared composites, thus contributing to much more electrons maintained on the conduction band of g-C3N4 with powerful reduction potential to easily induce reduction reactions and the enhanced photocatalytic performance. The present study offers valuable insights into designing of other fresh composites with efficient holes transfer, as well as an approach to resolve the low energy conversing efficiency of g-C3N4 in photocatalytic CO2 reduction and comprehensive ecological improvement.