Abstract:To determine the optimal process of Radix Astragali fermented by yeast.On the basis of single factor experiments，a four-factor three-level Box-Behnken central composite design was utilized for mathematical modeling for total flavonoids content as a response to fermentation time，temperature，inoculum concentration and initial pH，followed by responses surface analysis of the relationship between the function and the four variables.The effect order of the four factors on the preparation technology was fermentation temperature＞time＞inoculum concentration＞initial pH.The optimal fermenting conditions were fermentation time 9.46 d，fermen tationtemperature29.07℃，inoculum concentration 10.45%，initial pH 6.52.Undersuchcondition，theestimatted content of total flavonoids contents was 0.890 mg/mL，experiments were conducted after adjusting the fermentation conditions.The actual content was 0.866 mg/mL，lower than estimated content 2.70%.Optimization of fermentation process by response surface methodology was reasonable，this method can be used in practice.