Abstract: The resistance and dose limitation of tumors is a serious obstacle to cytotoxic drug therapy in the field of medical oncology. Nitric oxide (NO) is a powerful adjuvant for tumor hypersensitivity for traditional chemotherapy and radiation therapy. The concentration of NO plays an important role in affecting its anti-tumor effect. This review summarizes the mechanism of concentration-dependent effects of NO on tumor cells and the mechanism of chemotherapy sensitization. It provides evidence for rational use of NO to exert anti-tumor effects, and overcoming multidrug resistance and anti-tumor drug development.