Thyrotropin (TSH) is a hormone secreted by the adenoid pituitary gland that promotes thyroid hormone secretion, specifically through the hypothalamic-pituitary-thyroid axis, which regulates thyroid hormone secretion. The clinical application of thyroid stimulating hormone is mainly used in the following aspects: i. To determine pituitary function, thyroid stimulating hormone is secreted by the adenopituitary gland. When pituitary gland lesions or pituitary tumors occur, elevated thyroid stimulating hormone may occur, causing secondary hyperthyroidism. Second, thyroid stimulating hormone combined with T3 and T4 to determine thyroid function. Thyroid stimulating hormone is suppressed by T3 and T4. Hyperthyroidism can be diagnosed when T3 and T4 are increased and TSH is decreased. Hypothyroidism can be diagnosed when T3 and T4 are lowered and TSH is elevated. Third, to diagnose subclinical hyperthyroidism or subclinical hypothyroidism, thyroid stimulating hormone sensitivity is high, and when there is abnormal thyroid function, TSH changes before T3 and T4, which can be used to detect subclinical thyroid disease.