Abstract: Red kidney bean is a kind of valuable edible and medicinal soy food, which contains rich nutrients and a lot of effective ingredients. Polysaccharides are the main active component of red kidney beans, which have a variety of pharmacological effects such as anti-aging, anti-virus, anti-oxidant, antitumor and decreasing blood sugar and blood fat. In recent years, there have been substantial studies on the healthcare value, nutrition composition, product development of red kidney beans, but the extraction process of polysaccharides from red kidney beans and the analysis on its structure and biological activity have not been explored yet. The study respectively used enzyme's characteristics of effectively destroying the cell wall and keeping the activity of polysaccharide, etc, and the ultrasonic's characteristics of rapidness and energy saving by producing the effect of cavitation, shearing and intense mixing in liquid with the dispersion effect, to damage the cell tissue. By using the combined enzymatic and ultrasonic method assisted to extract polysaccharides out of red kidney beans, taking red kidney beans as raw material and polysaccharides yield as the index, and fixing the temperature at 50℃, the study firstly applied the L9(34) orthogonal experiments to screen out the best ratio of compound enzymes; and then on the basis of single factor experiment, the Plackett-Burman design was used to analyze solid-liquid ratio, amount of complex enzyme, pH value for enzyme hydrolysis, enzymolysis time, ultrasonic power and ultrasonic time, and these 6 factors were significant. Furthermore, the main factors affecting polysaccharides yield (pH value for enzyme hydrolysis, ultrasonic power, amount of composite enzyme and ultrasonic time) were investigated and optimized by response surface design using Box-Behnken center-united experiment software. Meanwhile, red kidney beans polysaccharide structure had been preliminarily analyzed by using ultraviolet spectrum and infrared spectrum scanning, together with analytical results of the glycosides. The results showed that the best ratio of compound enzymes for Papain, Pectinase and Cellulase enzyme was 3:1:3; among 6 factors, the influences of pH value for enzyme hydrolysis and ultrasonic power on the extraction of red kidney beans polysaccharides reached extremely significant effect, and amount of composite enzyme and ultrasonic time were the significant factors. For optimum technological parameters, i.e. solid-liquid ratio 80:1 mL/g, amount of composite enzyme 4.0%, pH value of 5.0 for enzyme hydrolysis, enzymolysis time 1.5 h, ultrasonic power 400 W and ultrasonic time 34.0 min, the yield of the polysaccharides of red kidney beans was 14.15%. Ultraviolet spectrum scan and infrared spectrum scan showed that after DEAE-52 chromatography column and Sephadesx G-200 cellulose chromatography column, red kidney beans polysaccharide had higher purification; the connecting way of red kidney beans polysaccharides was alpha (1→4) and (1→6) connection, which could be speculated by periodate oxidation and Smith degradation analysis. The results provide theory basis for further development and utilization of combined enzymatic and ultrasonic method in assisting to extract polysaccharides out of red kidney beans and subsequent research on red kidney beans polysaccharides structure characterization and biological activity.