Thyroid cancer can be classified into differentiated and undifferentiated types based on histology. Differentiated thyroid carcinoma can be classified as papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC), with the former accounting for 75% of all thyroid carcinomas and the latter 16%. Differentiated thyroid carcinoma expresses TSH receptors on the cell membrane surface and responds to TSH stimulation, causing thyroid cancer tissue to recur and proliferate. Suppression of serum TSH levels by supraphysiological doses of T4 reduces the risk of tumor recurrence. That is why postoperative patients are treated with long-term L-T4 replacement therapy. The aim is to supply the body’s thyroid hormone needs on the one hand and to suppress tumor recurrence on the other. To achieve these two purposes, the dose of L-T4 should be larger than the replacement dose for the treatment of hypothyroidism. TSH suppression therapy after thyroid cancer surgery is indicated for differentiated thyroid cancer, based on the principle of essentially complete blockade of endogenous TSH production, while TSH detection is based on morning blood draw. For patients in the high-risk group (<15 or >45 years of age; male; nodule diameter >100 px; extrathyroidal invasion; history of radiation exposure; history of thyroid cancer-related disease; positive cut margins; distant metastases; extensive metastatic lymph node envelope invasion in the cervical lymph nodes): TSH <0.1 mU/L. For patients in the low-risk group (15 years < age <45 years of age; nodule diameter <100 px. No history of radiation exposure; no history of thyroid cancer-related disease; negative cut margins; no distant metastases; no cervical lymph node metastases; no other infiltrative variants): 0.1mU/L