Iodine is one of the substances used in the synthesis of thyroid hormones, and thyroid cells concentrate 131I from the blood circulation by overcoming the electrochemical gradient through NIS. thyroid follicular cells, TA and high-functioning nodules of TMNG in patients with GD overexpress NIS and have a significantly higher uptake of 131I than normal tissue. The average range of beta rays emitted by 131I decay is 1 mm in the tissues, so almost all the energy of beta particles is released in the thyroid gland, which has less effect on the tissues and organs surrounding the thyroid gland. In 2-4 weeks after oral administration of 131I, pathological changes such as edema, degeneration, epithelial swelling with vacuole formation and follicular destruction can be seen in the thyroid tissue, and the damage in the central part of the gland is more obvious. 2-3 months later, changes such as lymphocyte infiltration, follicular epithelial cell detachment and fibrous tissue proliferation can be seen in the thyroid gland. The therapeutic effect can last for 2-3 months, or even longer, and the efficacy is usually evaluated only 3-6 months after treatment.