Abstract: Circadian rhythm plays a role in regulating life activities and contributes to periodicity, orderliness, and synergy in organisms. The Bmal1 gene is one of the core components of the circadian rhythm system; the level of Bmal1 expression differs between tumor and normal tissues. Studies have shown that Bmal1 plays different roles in different tumors. Therefore, understanding the role of Bmal1 in different tumorigenesis could provide a new theoretical basis for early detection or effective treatment of tumors. In recent years, with the in- depth studies on time- based approaches, chrono- chemotherapy, which combines pharmacokinetics and biotic rhythm, has become one of the important methods of tumor treatment. Radiotherapy at different times can lead to differences in radiosensitivity, which makes chrono-radiotherapy increasingly prominent in tumor treatment. In-depth studies on circadian rhythm in cancer biology could provide new perspectives for tumor treatment.