Autophagy differs from apoptosis and is independent of phagocytes by the appearance of autophagosomes, autolysosomes, and complete nuclei in the cell. This process significantly contributes to the antineoplastic effects of radiation. Radiation is an important strategy in cancer treatment; however, many types of cancer show radioresistance. The effects of radiotherapy are affected by factors, including the degree of tumor tissue hypoxia, the ability to repair DNA damage, and the presence of cancer stem cells. We review the relationships among autophagy, the three factors in cancer radiation, and the possible underlying molecular mechanisms. The therapeutic implications of these relationships and mechanisms in clinical settings are also discussed.