Since 1942, iodine 131 has been used to treat hyperthyroidism, and about tens of millions of cases of hyperthyroidism have been treated with iodine 131 at home and abroad. With the in-depth research on iodine 131 treatment for hyperthyroidism and the re-understanding of its advantages and disadvantages, iodine 131 treatment for hyperthyroidism has been accepted by more and more doctors and patients. In developed countries in Europe and America, iodine 131 has been adopted as the first choice for the treatment of hyperthyroidism, among which 80％ or more patients with hyperthyroidism in the United States are treated with iodine 131. In China, more and more patients with hyperthyroidism are treated with iodine 131, with an efficiency rate of over 98% and a cure rate of 70-80%. Iodine 131 only accumulates in the thyroid tissue and is not taken up by other tissues. The beta radiation emitted by iodine 131 has a range of only 1 mm, which can destroy the hyperfunctional thyroid tissue and reduce the size of the enlarged thyroid gland with minimal effect on the surrounding tissues. Radioactive iodine 131 treatment does not reduce the fertility of patients, is not carcinogenic, and has no adverse effects on offspring when used by women of childbearing age. Therefore, radioactive iodine 131 treatment for hyperthyroidism has the advantages of simple method, wide application, safety and effectiveness, short cure time, low cost and low recurrence rate. The main complication caused by iodine 131 treatment is hypothyroidism. One type of hypothyroidism is the transient hypothyroidism caused by iodine 131 treatment, which is mild and can disappear on its own after 6-9 months. The other type is permanent hypothyroidism. The incidence of hypothyroidism after iodine 131 treatment for hyperthyroidism reported at home and abroad varies greatly, which may be mainly due to the different dose, method and follow-up time of iodine 131 used by each family. It is an indisputable fact that the incidence of hypothyroidism is high with isotopic iodine 131 treatment for hyperthyroidism. However, hypothyroidism is not unique to iodine 131 treatment, but also occurs after antithyroid drug therapy and surgery. In 5221 cases of hyperthyroidism, 24.8 ％ of permanent hypothyroidism were reported at 2.7 years postoperative follow-up. It has been reported that eventually hypothyroidism will occur at a rate of 3 ％ per year, regardless of the method of treatment. Therefore, the development of hypothyroidism with iodine 131 therapy is not a serious negative consequence. On the contrary, long-term ineffective treatment of hyperthyroidism often brings serious complications, such as white blood cell decline, liver function damage, heart disease, mental depression, and in some people, aggravation of goiter and protruding eyes, and in middle-aged and elderly people, osteoporosis and peripheral pain, etc. Therefore, when hyperthyroidism patients choose the iodine 131 method of treatment, they do not need to worry too much about the possible occurrence of hypothyroidism as a result, and timely and complete cure of hyperthyroidism is the most important thing. Low thyroid function is easy to diagnose and treat. Once hypothyroidism is diagnosed, its treatment is relatively simple, using thyroid hormone (eugenol) replacement therapy to bring the patient’s thyroid hormone levels to normal. Since this treatment only adjusts the level of thyroid hormone to the normal range, it will not cause any damage to the patient’s liver or kidney function or hematopoietic system; nor will it affect pregnancy or breastfeeding. In conclusion, hypothyroidism after iodine 131 treatment is an objective condition, and it has always been the goal of nuclear medicine practitioners to reduce early onset hypothyroidism to an acceptable level while ensuring a high cure rate. The presence of hypothyroidism does not affect the fact that radioactive iodine treatment for hyperthyroidism is the most effective treatment for hyperthyroidism.