Objective To investigate the anti-tumor effect of Qiyusanlong decoction (QYSL) in the mice with Lewis lung cancer (LLC) and its effect on the expression of programmed death 1 and programmed death ligand 1 (PD-1/PD-L1). Methods The model of lung cancer subcutaneous allograft was established using LLC cells. The model mice were randomly divided into six groups: a model group, a chemotherapy group, three QYSL groups of high, middle and low doses, and a combined group, each group containing 8 mice. On the 11th day, the low-, middle- and high-dose QYSL groups were respectively given intragastric administration of 20.12, 40.24, 80.48 g/(kg.d) QYSL; the chemotherapy group were intraperitoneally injected with 0.4 mL cisplatin; the combined group were administrated with cisplatin and high-dose QYSL; the model group were administrated with the same amount of normal saline, once a day for 10 days. Tumor volume was examined and tumor growth curve was drawn. Tumors were weighed and tumor inhibition rates were calculated. The expressions of PD-1, PD-L1 mRNA and protein in spleens and tumor tissues of mice were detected by real-time quantitative PCR and Western blotting, respectively. Results Compared with the model group, the high-dose QYSL group could inhibit tumor growth with tumor inhibition rate being 23.86%; the tumor inhibition rate between the combined group and the chemotherapy group was equal. The high-dose QYSL could significantly decrease the expression of PD-1 mRNA and protein in spleen and inhibited the expression of PD-L1 mRNA and protein in tumor. The levels of PD-1 and PD-L1 protein in the combined group were obviously lower than those in the chemotherapy group, but the interaction effect of the other indicators had no statistical significance. Conclusion QYSL can moderately inhibit the growth of the transplanted tumor by decreasing PD-1/PD-L1 level.