Due to partial or total removal of the thyroid gland, patients with postoperative thyroid cancer usually require replacement supplementation with synthetic levothyroxine sodium (trade name Euthyroxine or Retis) or animal thyroid tablets to maintain serum thyroid hormone levels in a reasonable range. In addition, thyroxine can inhibit the level of thyroid stimulating hormone (TSH) produced by the pituitary gland through a negative feedback mechanism, producing a therapeutic effect on thyroid cancer by reducing recurrence and inhibiting progression. Therefore, reasonable administration of thyroxine is especially important for patients with residual, recurrent or metastatic thyroid cancer after surgery. Patients with post-operative thyroid cancer should take thyroxine under the guidance of their doctors for a long term and reasonable period of time, which is beneficial to their health, but the dosage should be differentiated according to the specific condition (risk classification) of the thyroid cancer patient and precisely adjusted according to the patient’s serum TSH level. Generally speaking, patients need to make thyroxine dose adjustment according to the following criteria: 1. High and intermediate risk patients should suppress TSH to less than 0.1mU/L; 2. Low risk patients should suppress TSH between 0.1-0.5mU/L; 3. Clinically cured patients should control TSH between 0.5-2.5mU/L. Patients with contraindications to thyroid hormone suppression therapy such as heart disease and osteoporosis are not suitable for the above criteria. For special cases, it is recommended to consult an experienced thyroid disease-related specialist.