Abstract: Contents of the soluble dietary fiber(SDF) and the insoluble dietary fiber(IDF) of mung-bean powder before and after fermentation by Bacillus subtilis BF7658 were compared and a marked increase in the content of SDF was found. Based on single factor experiments,the orthogonal test was conducted to determine the optimum conditions which were as follows:material and water ratio 1∶10(w∶v),inoculation amount 11%(w/w),fermentation time 24 h and temperature 34℃. Under these conditions,the content of SDF was up to 10.08%,a9.30% increase compared with that before fermentation of 0.78%.