Objective To optimize the processing condition of the extraction of Baphicacanthis cusiae ( Nees) Bremek. roots polysaccharides ( BCP) by ultrasound technology, and to provide the basis for the further development and study of BCP. Methods The extraction temperature, extraction time, liquid-solid ratio were used as the influence factors, and the yield of polysaccharides from Baphicacanthis cusiae roots was used as the evaluation index. On the basis of single-factor test, 3-factor and 3-level Box-Behnken test was designed for quadratic polynomial regression equation of the yield of polysaccharides. And then the response surface methodology was used for the optimization of process condition. Results The optimum extraction condition was as follows: extraction temperature was 60℃, extraction time was 35 min, and liquid-solid ratio was 24.5∶1 (V∶m, mL·g-1). Under the optimal condition, the yield of polysaccharides was 83.7 mg·g-1. Conclusion The method is simple, rapid and highly efficient, which will provide experimental basis for the development and application of Baphicacanthis cusiae roots polysaccharides.