Abstract：Objective：To investigate the effect of tetrastigma hemsleyani radix flavones on myeloid-derived suppressor cells(MDSCs)， prostaglandin E2(PGE2) and cyclooxygenase- 2(COX- 2) in mice with Lewis lung cancer and the possible mechanism of regulating immune function and reversing tumor immune escape in them．Methods：A total of 40 C57BL/6 mice were divided into the model group， the celecoxib group， the groups of high- dose， medium- dose and low- dose tetrastigma hemsleyani radix flavones(hereinafter referred to the high- dose， medium- dose and low- dose groups)， eight mice in each group．After successful establishment of mice with Lewis lung cancer for 24 hours，the high-dose，mediumdose and low- dose groups were respectively given the concentration of 100 mg/mL，50 mg/mL and 25 mg/mL solution of tetrastigma hemsleyani radix flavones by gavage；the celecoxib group was administrated with the concentration of 100 mg/ mL celecoxib solution by gavage and the model group with 0.9% normal saline by gavage．After 14 days，the mice in each group were sacrificed to calculate the tumor inhibition rate；the contents of MDSCs in mononuclear cell of the mice's spleen in each group were detected by flow cytometry，and the contents of COX-2 and PGE2 in peripheral blood were determined by Enzyme Linked Immunosorbent Assay．Results：Compared with those in the model group，the tumor volume and tumor weight were smaller in the other groups(P＜0.05)；the contents of COX-2 and PGE2 in peripheral blood and the proportion of MDSCs in spleen cells were decreased(P＜0.05)．Compared with that in the celecoxib group，the tumor volume in the lowdose group on Day 8，12 and 14 was larger(P＜0.05)，and tumor weight larger(P＜0.05)；the content of COX-2 and PGE2 in peripheral blood was larger(P＜0.05)；the tumor volume in the medium-dose group on Day 8 was larger(P＜0.05)，and the PGE2 content in peripheral blood was larger(P＜0.05)；the tumor volume in the high-dose group on Day 14 was smaller(P＜ 0.05)； the tumor inhibition rate was lower in the low- dose and medium- dose groups(P＜0.05)， and the proportion of MDSCs was larger(P＜0.05)． Conclusion： Tetrastigma hemsleyani radix flavones has anti- tumor effect， and the effect is related to the down-regulation of MDSCs，COX-2 and PGE2.