About 90% of thyroid cancer is differentiated thyroid cancer (DTC), including follicular thyroid cancer and papillary cancer. Currently, the best treatment method is: total or near-total thyroidectomy + radioactive 131 iodine therapy + thyroid hormone suppression therapy. Complete surgical resection is the main treatment for differentiated thyroid cancer and the most important factor affecting the prognosis. For differentiated thyroid cancer, except for low-grade malignant tumors less than 1 cm in diameter and confined to the thyroid gland, total or near-total thyroidectomy should be performed, and subtotal thyroidectomy and single lobectomy are not recommended. As serum thyrotropin stimulation can promote the growth of thyroid cancer cells, treatment with supraphysiologic doses of thyroid hormone can suppress serum thyrotropin levels, thus reducing the risk of recurrence of DTC. Postoperative radioactive 131 iodine therapy is an indispensable radical treatment. The basic principle is that 99% of the radiation released during the decay of 131 iodine is beta radiation. The treatment of DTC must be interviewed in a comprehensive way, and the use of one or two types of treatment alone will affect the long-term survival rate of patients. Indications for 131 iodine treatment: all stage III and IV patients, all stage II patients younger than 45 years old, and some stage II patients older than 45 years old. Stage I patients with one of the following conditions: multiple lesions, lymph node metastasis, extra-thyroidal (or vascular) infiltration, and higher malignancy. The dose of 131 iodine treatment for thyroid cancer is generally 100-200 mCi per dose, which is generally safe for patients.