Abstract:To determine the optimal conditions of solid fermentation of the Astragalus polysaccharides by Aspergillus niger.On the basis of single factor experiments，a three-factors three-levels Box-Behnken central composite design was utilized.On the mathematical modeling for polysaccharides content as response to fermentation time，fermentation temperature and inoculum concentration，followed by responses surface analysis of the relationship between the variables.The results showed that the factors influencing the content of Astragalus polysaccharides were fermentation temperature，fermentation time and inoculum concentration.The optimal fermenting conditions were as follows：fermentation time was 7.3 d，fermentation temperature was 28.5 ℃，inoculum concentration was 5%.Under such conditions，the actual average content after experiment was 84.74 mg/g，lower than estimated content 1.57%.The optimization of solid fermentation of Astragalus polysaccharides was obvious，which provide the certain experimental basis for deep research of Astragalus.