Usually, as long as thyroid cancer is found, surgical resection will be thought of, and surgery is an important means of thyroid cancer treatment. Yang Hui, Department of Nuclear Medicine, Henan Cancer Hospital Thyroid papillary and follicular cancers have low malignancy, low postoperative recurrence and metastasis rate, late recurrence and metastasis, so for a long time, the comprehensive treatment of thyroid cancer has not been paid enough attention. In some places, pure surgical treatment is adopted; in the better ones, thyroid hormone treatment is given after surgery; only big hospitals have special protective wards, which can carry out the three-step comprehensive treatment of “surgery + iodine 131 + thyroid hormone”. With the strengthening of international academic exchanges and the promotion of “surgery + iodine 131 + thyroid hormone” comprehensive treatment plan in China, the “three-step” treatment of thyroid cancer has been gradually popularized. It is found that thyroid cancer has the characteristic of multifocal, and it is impossible to completely remove thyroid cancer under the microscope during thyroid cancer surgery, and some thyroid tissues will always remain, and there may be tiny cancer foci in the residual tissues. After iodine 131 is absorbed by thyroid cells, the beta rays it emits can kill the residual thyroid tissues, and at the same time, it will also kill the tiny cancer foci in the residual thyroid tissues, therefore, the treatment of iodine 131 can achieve the purpose of reducing recurrence and metastasis. The results of bulk research show that the recurrence and metastasis rate of thyroid cancer is 34% after simple surgery, and the recurrence and metastasis rate is reduced to 2.7% after iodine 131 comprehensive treatment. Meanwhile, after the residual thyroid tissue was removed by iodine 131, thyroglobulin (Tg) became more sensitive and accurate in recurrent metastasis monitoring. Iodine 131 is also the best treatment for recurrent metastasis of papillary and follicular thyroid cancer, and is an excellent representative of molecularly targeted therapy with low toxicity and good efficacy. In addition, whole-body iodine 131 scanning is also a specific imaging method for early diagnosis of recurrent metastasis of papillary and follicular thyroid cancer, observation of iodine 131 uptake in the lesion during treatment, and determination of efficacy and prognosis. To summarize, Iodine 131 can be used for both examination and treatment, and it is a veritable “nemesis” of papillary and follicular thyroid cancer.