An ultralong SiC@g-C3N4 core-shell nanowires heterojunction photocatalyst was synthesized by the direct pyrolysis of melamine on the surface of SiC nanowires (NWs). The flexible heterojunction used as a photocathode for photoelectrochemical (PEC) water splitting shows a photocurrent density of - 0.62 mA cm(-2) at - 0.6 V vs Ag/AgCl in 0.1 M Na2SO4 solution, which is due to obviously enhanced visible light collection and charge separation. The photoexcited electrons on the lowest unoccupied molecular orbital (LUMO) level of g-C3N4 can be easily transported to the conduction band (CB) of SIC, whereas the photoexcited holes on the valence band (VB) of SiC can be transferred to the highest occupied molecular orbital (HOMO) level of g-C3N4. The synergic effect between SiC and g-C3N4 can decrease the recombination rate of photogenerated carriers and improve the photocatalytic hydrogen production activity. This work presents a novel SiC@g-C3N4 core-shell flexible photocathode for highly efficient PEC water splitting, which can be extended to fabricate various other flexible core-shell nanoheterostructures.