Abstract: Prostate cancer (PCa) is the most common urological malignancy in men worldwide, and its incidence is increasing annually. Radiotherapy is one of the main treatment methods for PCa. However, some patients still have recurrence, local progression, and even distant metastasis after receiving radical radiotherapy. As an emerging tumor treatment strategy, immunotherapy has made great progress in the treatment of various solid tumors. Owing to the inherent immune escape mechanism of PCa, the efficacy of immunotherapy is unsatisfactory. Therefore, new combined strategies must be explored to improve the efficacy of immunotherapy for PCa. With the in-depth study of the tumor immune microenvironment, the immunomodulatory effect of radiotherapy has gradually attracted attention. Researchers found that the immunomodulatory effect of radiotherapy depends on the dose. Low-dose radiotherapy can enhance tumor immunogenicity by remodeling the tumor microenvironment, whereas high-dose radiotherapy can further activate the innate immune signaling pathway by directly inducing the immunogenic necrosis of tumor cells. Therefore, the synergistic strategy of radiotherapy and immunotherapy has become a research hotspot. This work aims to review the regulatory effect of radiotherapy on PCa antitumor immunity, clarify the latest progress and potential clinical value of radiotherapy combined with immunotherapy, and provide a theoretical basis and new research directions for optimizing the combination immunotherapy strategies for prostate cancer.