The development and application of new anti-tumor selenium nano-radiotherapy sensitizer is a new strategy that uses selenium nanomaterials (selenium nanomaterials) as radiosensitizer (radiosensitizers) to produce a large number of reactive oxygen species (reactive oxygen species-ROS), so as to improve the sensitivity of tumor cells to radiotherapy and enhance the effect of radiotherapy. Selenium nanomaterials are nanomaterials with semiconductor properties that have highly biocompatibility, stability, tunability and functionality, which can be used in drug delivery, photothermal therapy, and photodynamic therapy. The new anti-tumor selenium nano-radiotherapy sensitizer can realize accurate radiation therapy of selenium nanomaterials with high atomic number, high X-ray absorption rate and high ROS production rate.