A mild anion exchange approach is proposed for the synthesis of alloyed Co-Fe bimetallic disulfide. Abundant structural disorders and tunable compositions are effectively induced by the anion exchange process. The alloyed Co-Fe bimetallic disulfide exhibits a low overpotential of 205 mV to reach a current density of 100 mA cm-2 in an acidic electrolyte, which is significantly improved compared to the performance of individual disulfide. It is believed that this work paves a new strategy for the synthesis of bimetallic compounds and highlights the importance of tuning the catalyst composition for achieving high catalytic performance.