Objective To investigate the status of IDD knowledge and prevention behavior of the residents in Gansu Province, so as to provide scientific basis for effective health education and health promotion. Methods The questionnaire was completed through Wechat push by university freshmen, and the questionnaire data was collected through the questionnaire Star platform. The knowledge, knowledge sources and prevention behavior were analyzed. Results A total of 2041 people were surveyed. The qualified rate of IDD knowledge was only 46.9%, in which 42.1% knew the main hazards of iodine deficiency disorders, 20.9% knew the most important basis for the implementation of universal salt iodization (USI) in China, 51.3% knew key groups with appropriate iodine nutrition, 61.9% knew that iodizing salt was the best iodine supplement, 62.3% knew that most of our external environments were iodine deficient. Male and those with lower income were more likely to believe that iodizing salt was the best iodine supplement (P<0.05). People with higher incomes were more likely to believe that USI prevents mental retardation in children and iodine is deficient in most of our external environments (P<0.05). The top four channels for acquiring IDD knowledge were television, internet, books and medical personnel, with slight differences among different cities and states. About 80.6% people insisted on eating iodized salt, and 19.4% did not insist on eating iodized salt. Non-iodized salt consumption reached 12.7% in high-income population, 11.1% in Lanzhou and 10.1% in Longnan. Among the people who didn’t adhere to eating iodized salt, 54.4% worried about thyroid disease caused by excessive iodine, and 37.3% bought salt according to the types of salt available in the market without paying attention to the iodine content of salt. Only 34.1% people ate iodine-rich food ≥4 times/month. The proportion of people who eat out ≥4 times/month was 25.2%. Conclusion The rate of IDD knowledge and the consumption rate of iodized salt and iodine rich food were low in Gansu Province. The opening of salt market, the fear of thyroid disease caused by excessive iodine, and the low IDD knowledge were the reasons for the decreasing iodized salt consumption rate. It is necessary to strengthen IDD health education and improve the understanding of salt iodization and scientific iodine supplement.