Abstract: Ultra-high dose rate (FLASH) radiotherapy is an innovation radiotherapy technique that has emerged as one of the revolutionary technologies in the field of radiotherapy over the past six years. It demonstrates excellent normal tissue protective effects without compromising the therapeutic efficacy on tumors. Moreover, the extremely short delivery time of FLASH radiotherapy helps eliminate the impact of organ or tumor motion on treatment accuracy, thereby enhancing treatment precision and patient comfort. This technology holds the potential to fundamentally transform the landscape of malignant tumor treatment. Currently, the underlying mechanism of the protective effects of FLASH radiotherapy on normal tissues are not fully understood. The authors present provide a comprehensive overview of the research progress in FLASH radiotherapy, encompassing both normal tissue protection and tumor treatment effects. Additionally, this paper provides insights into the potential biological mechanisms underlying the protection effects of FLASH radiotherapy. Consequently this paper serves as a valuable reference for further research in the field of FLASH radiotherapy.