Abstract: The crude viscera polysaccharides were extracted from Urechis unicinctus viscera by hot water extraction method . The effect of each factor such as the pH, the ratio of material to liquid, the time and the temperature on the extraction of the water-soluble polysaccharides in Urechis unicinctus viscera were investigated.using the methods of single factor test and orthogonal design test of L9(34).The scavenging action of Urechis unicinctus viscera polysaccharide on hydroxyl radical(?OH) was tested by Fenton system The results showed that the optimum extraction conditions were as follows: pH10, solid-liquid ratio 1:40, extracting time 3 h, extracting temperature 60 ℃. The scavenging capability of the crude polysaccharides to hydroxyl radical was reached to 60% at the concentration of 50 μg/ml and has dose effect.