The extraction of polyphenols from B. blakeana Dunn leaves by ultrasonic-assisted extraction was optimized. Based on single factor experiments, ratio of liquid to solid, ethanol concentration and pH were selected as independent variables，and the yield of polyphenols as response value, the experiment method was designed according to Box-Behnken central composite design with 3 factors and 3 levels, the effects of each independent variables and their interactions on the yield of polyphenols were studied. The mathematical regression model of the yield of polyphenols and each factor was established by using the Design-Expert software and the optimum condition was determined. The results showed ethanol concentration was the most significant factor to affect response value. The modified optimum extraction condition was ratio of liquid to solid 37∶1, ethanol concentration 74%, pH 6. Under the condition, polyphenols yield was 1.47%, which was basically the same as predictive value of 1.49% by the model, which meant the optimization of the extraction of the polyphenols from B. blakeana Dunn leaves by response surface methodology was reasonable and practicable.