Abstract: The process of tumor cells migrating from the primary lesion to distant sites to form metastatic lesions increases the mortality of patients. Radiotherapy can cause DNA damage directly through ionization or indirectly through the production of reactive oxygen species, thereby destroying tumor cells. However, recent studies have shown that radiotherapy-induced changes in tumor microenvironment can promote tumor metastasis and cause treatment failure in some cases. The relationship between tumor microenvironment changes after radiotherapy and tumor metastasis has received widespread attention, but the mechanism remains unclear. This review discusses how radiotherapy promotes tumor metastasis by inducing cytokine expression, hypoxia, increased integrin expression and changes in exosome.