In order to improve sulphur removal efficiency, deep eutectic solvent (DES) is first introduced into the fuel oil desulphurization process with sodium borohydride (NaBH4). Thereby, a novel method for fuel oil desulphurization by extraction coupled with reduction is proposed, where DES is used as stabilizer and extractant and NaBH4 is used as reducing agent. The nickel borides produced from NaBH4 and nickel salts were characterized using a particle size analyzer, surface area analyzer, and transmission electron microscopy. The results show that the nickel borides produced in DES have smaller particle sizes and a higher BET surface area than that in methanol/tetrahydrofuran (MeOH/THF). Sulphur removal efficiency using DES as medium was higher than that using MeOH/THF as medium. The effect of process parameters on the sulphur removal efficiency was investigated by orthogonal experiments. The results showed that the sulphur removal efficiency of dibenzothiophene can reach more than 96%. The desulphurization of dibenzothiophene should proceed over the cleavage of C-S bond to biphenyl and desulphurization reaction followed the pseudo-first-order reaction. The structures of the DESs remained unchanged after regeneration. In summary, the novel desulphurization method is feasible and promising.