Objective: We evaluated the effect of low-dose of ionizing radiation on thyroid function of medical occupational group with long-term exposure; furthermore; we analyzed the relationship between the thyroid hormones and the risk factors; such as exposure length; department. Ultimately; providing the scientific basis for setting the ionizing radiation protection standards. Methods: The population who engaged radiodiagnosis and radiotherapy in a tertiary-A hospital were set up as occupational exposure; 724 medical professionals as the research object. We figured out the basic information and general condition of the groups by face-to-face questionnaire survey; By means of the thyroid hormone testing; we analyzed the thyroid hormone levels with different population; occupational exposure factors. Then; 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. Applying Epidata、Excel in data management. All the data was analyzed by statistical software package Stata12.0. Descriptive statistics; single factor analysis of variance and other statistical methods were used for data analysis. Test standard: α=0.05、P<0.05 statistical significant. Results: 1. Based on the work experience; we divided the study population into four groups; such as 1-9; 10-19; 20-29; and>30 years. The difference of the TSH level among the four groups was statistically significant (P<0.05) . 2. The multiple logistic regression showed that sex and seniority were the independent risk factors for the abnormal rate of thyroid nodules. Conclusion: Long-term exposure to low-dose ionizing radiatiom could induce the thyroid damage of medical occupational population; which should be broader concerned.