In photocatalytic field, it is a significant challenge to synthesize cocatalyst with high performance, noble-metal free and facile methods to recycle. Herein, carbon layer coated Fe3C(Fe3C@C) nanoparticles were prepared by one-step method and for the first time utilized as highly efficient cocatalysts for improving visible-light-driven hydrogen evolution activity of g-C3N4. The photocatalytic hydrogen evolution rate of optimal Fe3C@C/g-C3N4 was about 27.2 times of bare g-C3N4 samples. Furthermore, the Fe3C@C/g-C3N4 composite catalyst showed excellent stability and reusability. The apparent quantum yield (AQY) of the optimized FeC@C/g- C3N4 reaches 0.501% and 0.124% at 400 nm and 420 nm, respectively. The AQY of the FeC@C/g- C3N4 is 26.2 times higher than that of g-C3N4 at 400 nm Fe3C@C has an extraordinary cocatalytic effect for g-C3N4 photocatalytic hydrogen evolution mainly due to three aspects: Firstly, the Fe3C acts as a trap to lure electrons because of its lower Fermi energy level and higher conductivity, which can increase the hydrogen production activity by trapping the photogenerated electrons produced by g-C3N4; Secondly, the coated carbon layer can provide chemical protection for Fe3C nanoparticles and promote the transfer of photogenic electrons, thus further improving the efficiency and stability of photocatalytic hydrogen production; Thirdly, the strong magnetic property of Fe3C@C nanoparticles gives Fe3C@C/g-C3N4 photocatalysts the advantages of low cost and high recovery efficiency. It is believed that this work provides a new strategy and possibility for the application of photocatalytic hydrogen production. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.