Abstract: Reactive nitrogen species (RNS) affects intracellular redox balance and induces post-translational modification of proteins. Moreover, RNS, as the signal molecule, participates in the transduction of cellular signals under physiological conditions. However, excessive RNS can induce nitrosative stress and then damage cells, and thereby may play a role in the tumor initiation and progression. Thus, we discussed the role of RNS under physiological conditions and the tumor microenvironment, which may provide some novel ideas for the development of new drugs and the treatment of diseases.