Abstract: The millet bran was used as the experimental material in this study. In order to increase the yield of the millet bran SDF,the method of ultrasonic-microwave cooperated with enzyme was used to modify the dietary fiber of the millet bran which was pre-processed by the method of steam explosion.The effect of the amount of enzyme,temperature,p H and the power of microwave were investigated separately.Besides,the Box-Behnken experiment was designed based on the result of single factor experiment,the process conditions of the modification of millet bran SDF was optimized by response surface methodology. The steam exploration condition was set as pressure equaled to 1.0 MPa and time equaled to 90 s,the optimal process parameters are set as: enzyme dosage was5.85%,temperature was 56 ℃,p H value was 4.64 and microwave power was 451 W.Under the condition above,the content of SDF was 13.117% which was 10.96% higher than the unmodified millet bran SDF.