Ultrafiltration membrane separation was used to purify xylooligosaccharides(XOS) from straw enzymatic hydrolysis.Protein,lignin removal rates and XOS transmittance were used as evaluation indices,the influence of feed concentration,operating pressure,temperature,and pH on the purification efficiencies were studied.Preliminary extraction conditions were studied by single factor experiment,and then optimized by Box-Behnken model.The results were: feed concentration 2.24 ° Bx,operating pressure 0.18MPa,temperature 25℃,pH 7.0.Under these conditions,XOS transmittance was 92.1%,protein removal rate was 67.9%,and lignin removal rate was 67.8%.The factors of ultrafiltration purification were analyzed by response surface method,the order of importance was: feed concentration,pH value,operating pressure,and operating temperature.This research provides reference for XOS purification process by ultrafiltration separation method.