Iodine 131 treatment is not needed after all thyroid surgeries, but if there are metastases of thyroid cancer and other conditions, it is needed. If the tumor has not spread in the early stage of thyroid cancer, iodine 131 treatment is generally not needed, and it is also generally not needed after non-tumor thyroid surgery. Radioactive iodine treatment is recommended if there are cases such as the tumor has obviously spread to tissues other than the thyroid gland, the malignant nodule is too large in size, or the tumor has invaded the blood vessels. The purpose of iodine 131 treatment is to destroy the tissues of the thyroid gland and reduce the production of thyroid hormones. Hypothyroidism is the most likely sequela of iodine 131 treatment, and there is also the possibility of radiation thyroiditis. Iodine 131 treatment should be used after thyroid surgery according to the doctor’s instructions and according to the condition of the patient.