In this study, Ultrasonic-Microwave assisted alkali (UMAA) was applied to extract water-unextractable arabinoxylan (WUAX) from the corn bran. The various factors including ultrasonic power, concentration of sodium hydroxide, solvent-to-material ratio and ultrasonic-microwave synergetic time were optimized by response surface methodology coupled with Box-Behnken design (BBD) on basis of the results of single factor experiments. The results showed that the maximum WUAX yield of 27.78 ± 0.17% was obtained with ultrasonic power 500 W, concentration of sodium hydroxide 0.30 mol/L, solvent-to-material ratio 30 mL/g, ultrasonic-microwave synergetic time 25 min. FT-IR analysis processed the characteristic peaks of polysaccharide. Chemical composition analysis indicted WUAX was mainly composed of xylose, arabinose, glucose, galactose, rhamnose, mannose, glucuronic acid and galacturonic acid, at a ratio of 38.3:28.2:22.3:5.1:2.5:0.7:1.5:1.4, respectively. In addition, the antioxidant activity assay in vitro showed that WUAX processed strong Fe2+ chelating activity and good scavenging effect on DPPH radical. These results clearly indicated the UMAA is an effective method for extraction of antioxidant WUAX from corn bran and the polysaccharides could be exhibited broad development and application prospects.