Abstract: DNA methylation plays an important role in biological processes. Balance of methylation warrants life activities such as regulation of appropriate gene expression and stability maintenance of genetic materials. Ionizing radiation can induce hypomethylation in whole genome and hypermethylation in part of genes in CpG islands, which is a potential trigger of cancer, aging, and decreased immune function. In this paper, we described the changes and the biological effects and possible mechanisms of ionizing radiation-induced DNA methylation abnormality, and also proposed some opinions to prevent ionizing radiation-induced methylation imbalance.