Abstract: In order to make full use of walnut by-products and reduce environmental pollution, walnut green husk was used as the research object. Polyphenols were extracted by different pH values (3,7,10) aqueous solution, 50% ethanol solution and Deep Eutectic Solvents (urea/choline chloride:DES-UC, oxalic acid/choline chloride: DES-OC). Firstly, under the conditions of temperature 80 ℃, liquid-solid ratio 25 mL/g, and molar ratio of Deep Eutectic Solvents (DESs) complexing agent 1.0, the extraction effect of DES-OC was better under 60 min. Subsequently, on the basis of single factor experiment, the response surface methodology was used to determine the optimal process parameters for the extraction of polyphenols from walnut green husk by DES-OC : the molar ratio of oxalic acid to choline chloride was 1.0, the temperature was 85 ℃, the time was 62 min, and the liquid-solid ratio was 50 mL/g. Under these conditions, the extraction amount of polyphenols was 50.87 mg/g. In addition, through the study on the antibacterial activity of the mixed solvent extracted from walnut green husk polyphenols, it was found that the antibacterial effect of DES-OC mixed with walnut green husk polyphenols on E.coli was better, followed by S.aureus and P.chrysogenum. The results can provide a theoretical basis for the research and development of natural antibacterial agents and preservatives, broaden the processing and utilization of walnut green husk, and also provide new ideas for the extraction of bioactive components from by-products of agricultural products.