The combination of photocatalysis with biorefinery and hydrogen (H2) production is highly desired, yet the systematical processes have not been achieved for the lack of development of an effective bifunctional photocatalyst to enhance the efficiency of biorefinery and H2 generation. Here, we reported an efficient photocatalyst to promote xylonic acid formation and H2 production by introducing cyano groups on graphitic carbon nitride (g-C3Nx). The obtained g-C3Nx could effectively absorb visible light with extended range by the tunable band structure. We also found that electrons and holes were effectively separated on the surface of g-C3Nx, enhancing the visible-light photocatalytic response and therefore increasing biorefinery and H2 production. The efficient amplification of xylonic acid synthesis indicated the possibility of xylonic acid via this photocatalysis.