Abstract： Radiotherapy and immunotherapy prove significant for cancer treatment presently. Despite therapeutic effects, they carry risks of adverse reactions. The survival rates and quality of life of patients with thoracic malignancies frequently fail to fulfill expectations after they receive radiotherapy combined with immunotherapy. A major reason for this is the occurrence of treatment-associated pneumonitis. To gain a deeper understanding of the pneumonitis induced by radiotherapy combined with immunotherapy for lung cancer, this paper reviews the pathogenesis, incidence, risk factors, differential diagnosis, and treatment of such pneumonitis.