Objective To explore the regulatory effect of astragalus polysaccharide (APS) on immune function in immunosuppressed mice, and to establish a set of feasible indexes of immunological regulation and evaluation system of polysaccharides. Methods Both Cytoxan (CTX)-induced immunosuppressed mice and normal mice were treated with astragalus polysaccharide (APS). Spleen index, thymus index, phagocytosis rate and phagocytic index of peritoneal macrophages were assessed, and the spleen and thymus tissues were examined by histology. The percentage of CD3⁺, CD4⁺, and CD8⁺ cells in peripheral blood were determined by flow cytometry. Results APS significantly increased the thymus and spleen indexes in both immunosuppressed mice and normal mice, promoted the histological development of spleen and thymus in normal mice, enhanced the recovery of histological structures in the spleen and thymus in the CTX-induced immunosuppressed mice. APS also enhanced the phagocytosis rate and phagocytic index of peritoneal macrophages in both immunosuppressed mice and normal mice. In addition, the percentage of CD3⁺ and CD4⁺ cells,the ratio of CD4⁺/CD8⁺ in peripheral blood of both CTX-induced immunosuppressed mice and normal mice were increased while CD8⁺ cells were decreased. Conclusions The results of this study suggest that astragalus polysaccharide can improve the non-specific immunity and cellular immunity in mice, and indicate that we established comprehensive evaluation indexes of immunoregulatory effects of polysaccharides.