Objective The prevalence and its influencing factors were analyzed in a medical occupational population long-term exposure to low-dose of ionizing radiation in order to provide evidences for occupational health protection of this kind of population. Methods The population who engaged radiodiagnosis and radiotherapy in a tertiary-A hospital was set up as occupational exposure, and the administrative staffs in a company were considered as control. We figured out the basic information and general condition of the groups by face-to-face questionnaire survey, calculated the annual comulative radiation dose through local center for disease control and prevention, and obtained the prevalence of thyroid nodules by the thyroid ultrasound. Besides, we used the logistic regression model to analyze the risk factors related to thyroid nodule. Results Age, sex and seniority were proportionality between exposure and control groups. The dosages of occupational population exposure to ionizing radiation were about 1/10 of national permit value, belonging to low-dose exposure. However, the abnormal rate of the thyroid nodules in exposure group was significantly higher than that in control group, and the abnormal rate increased in trend with the annual comulative radiation dose and the exposure length (Ptrend<0.05). In addition, the multiple logistic regression showed that the annual comulative radiation dose and the exposure length were the independent risk factors for the abnormal rate of thyroid nodules, especially the annual comulative radiation dose (OR=16.913, 95%CI: 2.212-129.336). Conclusion Long-term exposure to low-dose ionizing radiatiom could induce the thyroid damage of medical occupational population, which should be broader concerned.