A thin porous film inorganic-organic heterostructure photocathode has been successfully fabricated and applied in photoelectrochemical (PEC) water splitting. Our work optimized the best structure of CuBi2O4 (CBO) base on FTO (fluorine doped tin oxide). Furthermore, it was passivated with polythiophene (PTh), a kind of conducting polymers of excellent environmental and thermal stability, to decrease the capture ability of surface state for photogenerated charge. Benefiting from the high light capture rate of porous structure of CBO and low electron-hole recombination rate of CBO/PTh heterojunctions, the as fabricated FTO/CBO/PTh electrode delivers excellent PEC performance with a ultimate photocurrent density of 0.41 mA cm(-2) at 0.3 V vs RHE (reversible hydrogen electrode) doubled to that of pure FTO/CBO electrode, which would be due to the significantly improved light absorption and rapid separation efficiency. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.