Polysaccharides was extracted from Tricholoma mongolicum mycelium. The effect factors, including ultrasonic power, ultrasonic time, liquid-solid ratio and temperature, were optimized through orthogonal tests L₉(3⁴) on the basis of single factor experiment. Results showed that ultrasonic power 18% (rated power 900 W), ultrasonic time 20 min, liquid-solid ratio 401 and extraction temperature 75 ℃. Under optimal conditions, the extraction yield of polysaccharides was 13.96%.