Iodine 131 is used to treat hyperthyroidism. The main mechanism of action is radioactive 131 iodine, which is ingested by thyroid cells into the thyroid gland, releasing a 2mm ray. It destroys the thyroid tissue cells and reduces the production of thyroid hormones, thus achieving the purpose of treating hyperthyroidism. It is mainly applied to the recurrent recurrence of hyperthyroidism, oral thyroid medication, which can cause allergy or liver function damage, leukopenia, hyperthyroidism combined with liver and kidney insufficiency and cardiac insufficiency. Contraindications are contraindicated in pregnant and lactating women, children and adolescents. The main side effect is to cause hypothyroidism, which requires lifelong oral eugenol replacement therapy. Before treatment of hyperthyroidism with iodine 131, it is necessary to discontinue antithyroid medications for at least two weeks to ensure adequate uptake of iodine 131 by the thyroid cells, and thyroid imaging is routinely performed before treatment to calculate the size of the thyroid gland as well as iodine uptake rate of the thyroid gland, to assess the iodine uptake capacity of the thyroid gland.