Thyroid cancer can bring considerable impact on life. Therefore, it is important to learn more about the causes of thyroid cancer and do a good job of prevention so as to stay away from the disease. The incidence of thyroid cancer in women is 5 to 6 times higher than that in men, suggesting that maybe gender factors are related to the development, but no evidence of estrogen stimulating tumor cell growth has been found. Like other malignant tumors, it is difficult to be sure of the factors of thyroid cancer development. Radiation, excessive or insufficient iodine, genetic inheritance, excess nutrition, bad emotion and hormone level may be the triggers of thyroid cancer development. Radiation cancer mostly occurs after external x-ray exposure. It is also important to note that the risk of thyroid cancer decreases with increasing age of radiation exposure, i.e., the risk is higher in young children than in adults. The younger the irradiated child is, the higher the risk of cancer. In addition, it is generally higher in females than in males. There is no conclusive evidence that excess iodine causes thyroid cancer, but iodine deficiency can also cause many thyroid disorders. Therefore, we recommend a balanced diet with no need for deliberate supplementation or no supplementation. Given that most thyroid cancer patients are currently in iodine-rich areas, it is recommended that postoperative thyroid cancer patients have an appropriate low iodine diet, then there is no need to routinely consume non-iodized salt.