NOVELTY - Chitosan modified cotton fiber is prepared by pumping 0.5-2 mass% sodium hydroxide pretreatment solution to pretreatment tank, dispersing cotton fibers in pretreatment tank with ratio cotton fiber:pretreatment liquid of 1 kg:8-15 L, stirring at 85-100 degrees C for 0.5-1.5 hours, collecting pretreated cotton fiber and waste pretreatment liquid, adding distilled water to pretreated cotton fiber with ratio cotton fiber:distilled water of 1 kg:8-15 L, cleaning, centrifuging at 500-1500 rpm to obtain cotton fiber and supernatant, mixing supernatant with waste pretreatment liquid, and neutralizing.    USE - Preparation of chitosan modified cotton fiber for textiles, medicine, and food.    ADVANTAGE - Preparation of chitosan modified cotton fiber has antibiosis property, lasting dyeing performance, good tensile force retention rate, and improved use life, and preparation is environment-friendly and has mild reaction condition, strong specificity, simple operation, and low cost.    DETAILED DESCRIPTION - Chitosan modified cotton fiber is prepared by pumping 0.5-2 mass% sodium hydroxide pretreatment solution to pretreatment tank, dispersing cotton fibers in pretreatment tank with ratio cotton fiber:pretreatment liquid of 1 kg:8-15 L, stirring at 85-100 degrees C for 0.5-1.5 hours, collecting pretreated cotton fiber and waste pretreatment liquid, adding distilled water to pretreated cotton fiber with ratio cotton fiber:distilled water of 1 kg:8-15 L, cleaning, centrifuging at 500-1500 rpm to obtain cotton fiber and supernatant, mixing supernatant with waste pretreatment liquid, neutralizing, discharging, adding distilled water to reaction tank, stirring at 60-120 rpm, heating with steam to 80-100 degrees C, adding chitosan oligosaccharide with molecular weight of 1000-3000 Da and ratio chitosan oligosaccharide:distilled water of 1 kg:10-20 L, stirring to dissolve for 30-60 minutes to obtain 0.05-0.1 kg/L chitosan oligosaccharide solution, adjusting pH to 3-4 using dilute hydrochloric acid, adding epichlorohydrin for 30-60 minutes with stirring speed of 50-120 rpm and ratio chitosan oligosaccharide:epichlorohydrin of 1 kg:0.3-0.5 kg, refluxing and reacting for 1.5-2.5 hours, adjusting pH to 9-10 using sodium hydroxide solution to obtain hydroxypropyl chitosan oligosaccharide solution, sending into etherification reactor, adding chitosan fiber with ratio cotton fiber:hydroxypropyl chitosan oligosaccharide solution of 1 kg:6-8 L, introducing 10-30 L/minute air, stirring and bubbling, adjusting pH to 9-10 using dilute sodium hydroxide, refluxing and reacting at 90-100 degrees C for 4-6 hours, adding ethylene glycol diglycidyl ether, butanediol diglycidyl ether, or hexanediol diglycidyl ether dropwise for 30-60 minutes with mass ratio chitosan oligosaccharide:diglycidyl ether of 1 kg:0.3-0.5 kg, refluxing and reacting for 1-2 hours, cooling with water to room temperature, discharging, centrifuging at 500-1500 rpm, collecting modified cellulose ether compound, concentrating supernatant in vacuum, mixing with hydroxypropyl chitosan oligosaccharide solution, reusing, sending modified cellulose ether compound to tunnel dryer, baking at 110-130 degrees C with transmission speed of 0.1-0.5 rpm for 0.5-2 hours, cleaning with distilled water with ratio cotton fiber:distilled water of 1 kg:8-15 L, centrifuging at 500-1500 rpm, sending precipitate to tunnel dryer, processing at 60-70 degrees C with transmission speed of 0.5-0.1 rpm for 0.5-1 hour to obtain modified cotton fiber with grafting rate of 3.28-5.9%, tensile force retention rate of 95.6-98.2%, and Escherichia coli inhibition rate of 34.5-45.3%, collecting supernatant, performing biological treatment, and discharging.