Electrooxidation of 5‑Hydroxymethylfurfural (HMF) is considered a promising strategy for replacing the sluggish oxygen evolution reaction (OER) of electrolytic water, which can reduce the consumption of hydrogen production and the risk of gas mixing and obtain value-added products. Herein, a nanosheet with nanoflower catalyst (H-0.3Co-Ni₃S₂) was synthesized via a one-step hydrothermal process with the assistance of hydrogen peroxide (H₂O₂) for the electrooxidation of HMF. Adding H₂O₂ and Co can decrease Ni's outer layer electronic cloud density, which benefits the catalyst's oxidation and catalyzes the HMF electrooxidation. H-0.3Co-Ni₃S₂ shows the superior performance of the HMF electrochemical oxidation with the initial potential of 1.25 V vs. RHE and the voltage of 1.38 V vs. RHE at 200 mA cm⁻² under the electrolyte of 1 M KOH with 10 mM HMF. The conversion rate, yield and Faraday efficiency of HMF electrooxidation for H-0.3Co-Ni₃S₂ in the electrolyte of 1 M KOH with 10 mM HMF are 98.2 %, 97.6 % and 97.6 %, respectively. Besides, we provide a novel stepwise electrolysis strategy that can inhibit OER effectively while electrolyzing large-concentration HMF rapidly. Finally, in an electrolyte of 1 M KOH with 30 mM HMF, the conversion rate, yield and Faraday efficiency achieve 100 %, 91.9 % and 97.4 %, respectively.