〔Abstract〕 Objective To investigate the effect of Qiyu Sanlong Decoction(QYSLD) on inhibiting lung cancer by regulating tumor immune microenvironment through PD-1 signaling pathway and on Th1 immune response in lung cancer bearing mice. Methods Lewis lung cancer cell line(LLC) was used to model subcutaneously implanted tumor in mice. 72 mice were randomly divided into Control group(n=18), cisplatin group(n=18), QYSLD group(n=18) and combined group(n=18).The general survival of mice was observedand recorded; the specific Th1 cell response to tumor antigen was detected by ELISA method; the proportion of PD-1 positive cells and the apoptosis of memory CD4+T cells in spleen T cells of mice were detected by flow cytometry; and the number and volume of pulmonary metastatic nodules were counted under an anatomical microscope after 21 days of continuous treatment. Results QYSLD could improve the general survival of mice bearing lung cancer, up-regulate the immune response of CD4+T cells and the specific killing effect of CD8+T cells. The proportion of apoptotic cells in PD-1 positive cells and CD4+memory T cells in spleen T cells of mice was down-regulated, and lung metastasis of mouse tumor cells was inhibited. Conclusion QYSLD can improve the survival status of mice bearing lung cancer and enhance Th1 immune response by mediating PD-1 signaling pathway, improve immune function and inhibit immune escape of tumor cells, thus inhibiting the metastasis of lung cancer.