To enhance the efficiency of the extraction for Epimedium koreanum Nakai polysaccharides, we conducted the Box-Benhnken experiment and examined the response surface. C57 BL6 mice were used as Lewis-bearing mice model in the study of the polysaccharides in the regulation of tumor immunity. In the first place, different factors including extraction time, temperature, and ratio were evaluated in the yield of polysaccharides. The second order polynomial equation was formed to fit the experimental data. The optimal condition was temperature 87 ℃, extraction time 3.84 h, and ratio of solution and material 1:16.33 to get polysaccharides from Epimedium koreanum Nakai. Under this condition, model-predicted and experimentally measured values of polysaccharide yield were 1.045% and 1.023%, respectively, with a relative error between them at 2.15%. The extraction method is reliable, simple and applicable to the extraction of Epimedium polysaccharides. In addition, this data suggests that Epimedium polysaccharides have obvious immune-regulatory activities in the tumor-bearing mice through increasing the immune-enhancing cytokines to override the immune- suppressing factors.