Myeloid-derived suppressor cells (MDSCs) are a group of cells with potent immune suppressive activity which have emerged as an important contributor to tumor progression and genesis. More and more clinical researches have found that accumulation of MDSCs in peripheral blood and tumor tissues could predict dismal outcome for patients with malignancies, which was a potential prognostic tumor marker. In addition, immunosuppression inducedMDSCs could reduce the efficacy of anti-tumor therapies. Therefore, better understanding the mechanism of MDSCs’ immune suppression in tumor microenvironment can provide reference for exploring new immunotherapies.