The human microecology, especially the intestinal flora, is a new dynamic organ of the human body. The intestinal flora and its metabolites can directly act on the intestine or indirectly through the microbiota⁃gut⁃organ axis to act on the whole body tissues and organs and play an important role. The main physiological functions of human microecology include: regulating gastrointestinal movement and digestion, intestinal barrier, regulating immune homeostasis and inflammatory response, material metabolism, cell differentiation and turnover, and cognitive behavior. Radiotherapy can cause significant changes in the human microbiota, manifested as changes in flora diversity and abundance. These changes are not only related to the efficacy of radiotherapy, but also closely related to radiotherapy injury, complications and prognosis.At the same time, it was found that there were gender differences in radiation efficacy and injury, which was related to the gender differences of intestinal flora. Therefore, maintaining and adjusting the human microecological balance has an important impact on the efficacy of tumor radiotherapy and the prevention and treatment of radiation damage and complications. The application of microecological preparations (probiotics, prebiotics and postbiotics) and faecal microbiota transplantation play an obvious role in reducing tissue and organ damage caused by radiation, improving the curative effect of radiotherapy and reducing complications. As an adjuvant anti⁃tumor therapy, it shows a good clinical application prospect. Therefore, the optimal combination and application of disease⁃specific and individualized probiotics will be an important research direction in the future.