To alleviate the environmental pressure caused by waste cotton straw and improve the utilization of cotton straw by-products, this paper used ethylene glycol solvent to separate lignin from cotton straw, the effects of various factors on its separation effect were studied, and the properties of the extract and its effect on the antioxidant capacity of PP were analyzed. The results show that the highest yield of 84.58% could be achieved by treating cotton straw with 0.8 mol?L-1 ethylene glycol solution for 1h at 160℃. The lignin modification has little effect on the crystallization properties and melting and crystallization temperatures of PP, but has an effect on its oxidation induction time, rheological properties, and mechanical properties: when 0.5wt% of lignin is added to PP, the oxidation induction time is increased by 38.3% compared with that of pure PP specimens, the shear torque is 25.58% higher in micro mixing rheological test, the elongation at break is 9.34% lower, and the impact strength has no change. It indicates that the lignin extracted by the ethylene glycol method can effectively exert an antioxidant effect in PP.