Abstract： Objective： To observe the effect of Shenmai injection on immune function in patients with lung cancer undergoing chemotherapy. Methods：A total of 70 cases of patients with lung cancer were divided into the control group and the study group according to the random number table method，35 cases in each group. The control group was given routine chemotherapeutic regimens with gecitabine and cisplatin， and the study group was additionally treated with Shenmai injection based on the treatment of the control group. Results：Before treatment，there was no significant difference being found in the comparison of the levels of innunoglobulin(Ig)G， IgA and IgM between the two groups(P＞0.05). After treatment，the levels of IgG，IgA and IgM in the study group were higher than those in the control group(P＜0.05). Before treatment，there was no significant difference being found in the comparison of the levels of CD4+，CD8+，CD4+/CD8+ and natural killer(NK) cell between the two groups(P＞0.05). After treatment，the levels of CD4+，CD4+/CD8+ and NK cell in the study group were higher than those in the control group，and the CD8 + level was lower，differences being significant(P＜ 0.05). Before treatment，there was no significant difference being found in the comparison of the levels of interleukin-6(IL-6)， interleukin-10(IL-10)，interferon-γ(IFN-γ) and tumor necrosis factor-α(TNF-α) in serum between the two groups(P＞0.05). After treatment，the levels of IL-6 and IL-10 in the study group were lower than those in the control group，and the levels of IFN- γ and TNF- α were higher(P＜0.05)， differences being significant. During treatment， the incidences of nausea and vomiting，and decreases of white blood cells and platelets in the study group were lower than those in the control group，the difference being significant(P＜0.05). Conclusion： Shenmai injection combined with routine chemotherapy can get a good curative effect in treating lung cancer， improve immune function and levels of T- lymphocytes， improve levels of inflammatory factors.