The invention discloses a Chinese yam polysaccharide extracting method. The method comprises the following steps: 1) taking fresh Chinese yam as a raw material, peeling, stripping and slicing; 2) adding an extracting solution, and pulping to obtain Chinese yam homogenate; 3) centrifuging the Chinese yam homogenate to obtain Chinese yam homogenate centrifugal supernatant; 4) filtering the Chinese yam homogenate centrifugal supernatant to remove starch in order to obtain filtrate; 5) adjusting the pH of the filtrate, and performing magnetic stirring to obtain a suspension; 6) centrifuging the suspension, and precipitating Chinese yam proteins; 7) adjusting the ultrafiltration pH, ultrafiltration temperature and ultrafiltration pressure intensity of the supernatant to perform ultrafiltration; 8) performing vacuum freeze drying on an intercepted part to obtain a Chinese yam polysaccharide. In the Chinese yam polysaccharide extracting method, the Chinese yam polysaccharide is extracted by an ultrafiltration concentration method, so that the polysaccharide extracting rate is up to 88.69 percent; moreover, the method is easy to operate, and is easy to implement. As proved by component measurement, infrared spectrum analysis, scanning electron microscope analysis and antioxidant activity measurement, the purity of the Chinese yam polysaccharide is 43.84 percent, and high antioxidant activity is achieved.