Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of cells of myeloid origin that comprises myeloid progenitor cells and immature macrophages, which expand in tumorbearing mice and patients' bone marrow, spleen and peripheral blood and recruit to the tumor site. MDSC express high levels of arginase 1 (ARG1), inducible-nitric oxide syntheses (iNOS), reactive oxygen species (ROS) and peroxynitrite. They could suppress T-cell functions by cell contact or not, and induce regulatory T cells (Treg), all of the above are its weapons to defend individuals' immune system. Anti-tumor strategies targeted at MDSC develop rapidly now. In this review, we briefly introduce the strategies that targeted at MDSC and their mechanisms.