In order to improve the processing characteristics (particle size, powder characteristics, color) and maintain the active substances such as deoxynojirimycin(DNJ), total polyphenols, total flavonoids and anthocyanins, the low-sugar mulberry extract powder with good nutrition and appearance quality was prepared by microbial fermentation technology. Two kinds of low-sugar mulberry extract powders (with or without soybean addition) were prepared by fermentation of mulberry protoplasm through Leuconstoc mesenteroides and Saccharomyces cerevisiae and freeze-drying. The processing characteristics and active substance contents of the low-sugar mulberry extract powder were compared with that of the mulberry powder directly crushed by dry mulberry. Compared with mulberry powder, the glucose content, fructose content, water content, water activity, hygroscopicity, bulk density, resting angle and particle size of two kinds of low-sugar mulberry extract powder were significantly decreased after fermentation and freeze-drying, and their processing properties such as color and fluidity were significantly improved. The DNJ content of mulberry powder was 0.68mg/g, which was significantly increased to 2.07mg/g after fermentation, 1.39mg/g after freezing-drying, and 1.03mg/g after freezing-drying and addition of soybean. The contents of total polyphenols and total flavonoids were not significantly affected by fermentation, freezing-drying and addition of soybean. The total polyphenols contents of mulberry powder, fermented mulberry, freeze-dried fermented mulberry, freeze-dried fermented mulberry with soybean addition were 27.70,8.55,5.83, and 25.85mg/g, and the contents of total flavonoids were 1.24,1.01,1.16 and 1.30mg/g, respectively. The content of anthocyanin decreased significantly after fermentation, while the content of anthocyanin did not change significantly after freezing-drying and soybean addition. After fermentation and freezing-drying, the processing characteristics of low-sugar mulberry extract powder were improved. The content of DNJ was increased, and the content of anthocyanin was decreased. However the contents of total polyphenols and total flavonoids were not significantly changed.