The thyroid gland is an important endocrine gland in the body, capable of secreting thyroid hormones, and thyroid function is regulated by the hypothalamic-pituitary-thyroid axis. The significance of thyroid function tests are as follows: First, to determine the functional status of the thyroid gland. When the body has symptoms of high or low metabolism, there may be hyper- and hypothyroidism, and thyroid function needs to be checked to determine the diagnosis. Second, identify the cause of hyperthyroidism and hypothyroidism. Whether hyperthyroidism or hypothyroidism, there are primary and secondary causes of the disease. Primary refers to the thyroid gland, while secondary refers to pituitary or hypothalamic lesions. Third, determine the functional status of thyroid nodules. The high incidence of thyroid nodules requires that the functional status of the thyroid gland be taken into account during clinical treatment. Fourth, detection of subclinical hyperthyroidism and hypothyroidism, especially subclinical hypothyroidism, is significant in pregnant patients. Fifth, both hyperthyroid and hypothyroid patients need regular rechecking of thyroid function and adjustment of medication dose during the treatment process.