Oat bran was used as the raw material， the modified Oat bran dietary fiber（OBDF） was processed by microwave method. The structure of OBDF before and after modification was studied by scanning electron microscopy （SEM）， X-ray diffraction （XRD） and fourier transform infrared spectra （FT-IR）. The functional properties changes were measurement by adsorption， solution， as well as scavenging ability of DPPH· free radical and hydroxyl radical. The results of SEM showed that modified OBDF appeared porous network structure， specific surface increased and microstructure were obvious changed. X-ray diffraction results showed that the modified OBDF crystal structure retained the original cellulose type Ⅰ structure， crystalline domain of OBDF after modification increased. FT-IR results showed that the characteristic absorption peak in the infrared spectrum was not changed significantly， but the intensity was decreased. The results of absorbent abilities showed that the modified OBDF and soluble dietary fiber（SDF） on cholesterol（under the condition of pH 7.0）， sodium nitrite， glucose， and oil were significantly increased than before modification （P<0.05）. The results of solubility showed that temperature and pH had great influence on the solubility of dietary fiber， under the condition of 70 ℃ and simulated stomach environment of human（pH 2.0）， the solubility of OBDF was reached to （0.14±0.02） g/mL. The modified OBDF showed better scavenging ability for DPPH· free radical and hydroxyl radical， and the scavenging ability of modified OBDF and SDF on hydroxyl radical reached up to 49.8% and 62.1% respectively.