A large number of epidemiological data have shown that, the incidence of radiation-induced cancer in a certain range of radiation dose is linearly related with exposure doses. And the dose ranges that people received during performing some of radiation therapy and medical radiological diagnosis are highly consistent with dose ranges where an increased risk of cancer groups was found by epidemiological investigation. With an increasing application of radioactive diagnostic and therapic equipments in disease diagnosis, treatment and healthy checks the potential health hazards due to radiation among a large number of patients and individuals performing healthy check should erect more concern. In risk assessment caused by medical radiation following the LNT model assumes at present still has a scientific and practical significance to reduce hazards.