Objective: This study was to investigate the effect of the Chinese herbal compound Kanggan granule (KG) on immune function in a mouse model of immunosuppression and its possible mechanism of action. Method: ICR mice were randomly divided into a normal control group (untreated non-immunosuppressed, Control), untreated immunosuppressed group (Model), positive control group (immunosuppressed and treated with 1.6 g/kg astragalus granule [AG]), high-dose KG group (immunosuppressed and treated with 24 g/kg, KG-24), and low-dose KG group (immunosuppressed and treated with 6 g/kg, KG-6). Each group received intragastric administration once daily for 7 days. Immunosuppression was induced by an intraperitoneal injection of dexamethasone (25 mg/kg) once daily beginning on day 1 for 3 days. To illuminate the mechanism of immunomodulatory, we studied the effects of KG on nonspecific immunity, humoral immunity and cellular immunity in mice respectively. Results: KG improved organ weights and improved the phagocytic ability of mononuclear macrophages in immunosuppressed mice (p < 0.01 or p < 0.05). The proliferation of spleen lymphocytes and number of peripheral blood leukocytes were enhanced after KG treatment in immunosuppressed mice (p < 0.05). KG increased the CD4 + /CD8 + ratio in immunosuppressed mice (p < 0.01) and increased serum IL-2 and IgG levels (p < 0.01). Conclusions: KG can improve immune function in immunosuppressed mice. Nonspecific immunity, humoral immunity, and cellular immunity were all enhanced.