To investigate the antitumor and immunomodulatory effects of Kang'ai Injection and its components in lung cancer-bearing mice through in vivo experiments.Methods:Male C57BL/6J mice were randomly divided into the following five groups:blank group，model group，low-dose group，medium-dose group，and high-dose group.All groups，except the blank group，underwent subcutaneous lung cancer-bearing model induction.Mice in each group were intraperitoneally injected with the following treatments once daily for 28 days:Kang'ai Injection at doses of 25 mg/(kg·d)(low-dose)，50 mg/(kg·d)(medium-dose)，and 75 mg/(kg·d)(high-dose).The body weight and tumor size of the mice were measured every 3 days.On the 17th and 27th days after modeling，in vivo imaging was used to observe tumor progression.On day 29，mice were sacrificed for further analysis.Hematoxylin and eosin(HE) staining was performed to observe lung metastasis.Flow cytometry was used to detect the proportions of CD3+，CD4+，CD8+ T lymphocyte subsets and regulatory T cells(Treg).Immunohistochemistry was used to assess Treg cell levels in tumor tissues.The optimal therapeutic dose of Kang'ai Injection was selected，and based on its composition，the Renshen-Huangqi extract group and the oxymatrine group were set up and also treated same as above.Serum levels of interleukin-10(IL-10)，interleukin-12(IL-12)，and interferon-γ(IFN-γ) were measured using flow cytometric cytokine bead array(CBA) assay.Results:The tumor weight and lung weight in the low-dose，medium-dose，high-dose，and Renshen-Huangqi extract groups were significantly lower than those in the model group(P<0.05)，and histological analysis showed reduced lung metastasis，with the medium-dose group showing the highest inhibition rate.Compared with the model group，the groups treated with Chinese medicine showed significantly increased proportions of CD3+ and CD4+ T cells(P<0.05).The proportion of Treg cells in the spleen and tumor microenvironment was significantly lower in the Chinese medicine-treated groups than the model group(P<0.05).In the oxymatrine group，IL-10 levels were reduced，while the Renshen-Huangqi extract group showed elevated IFN-γ levels.The medium-dose group of Kang'ai Injection showed increased IL-12 levels(P<0.05).Conclusion:Kang'ai Injection can inhibit the growth and metastasis of lung cancer in mice and improve immune function.This effect is related to the regulation of Treg cell proportions in the tumor microenvironment.Among the components，the Renshen-Huangqi extract plays an important role in immunomodulation.