Hypothyroidism (hypothyroidism) is a common disease in endocrinology. The main cause is the inability of the thyroid gland to produce thyroxine to meet the normal metabolic needs of the body. The National Health and Nutrition Examination found that about 1 in 300 Americans have hypothyroidism, and the incidence of hypothyroidism is on the rise as serum thyroid stimulating hormone (TSH) increases with age, and is significantly higher in women than in men. The prevalence of secondary hypothyroidism is <5%, while primary hypothyroidism is more commonly encountered in clinical practice. The main causes of hypothyroidism are the thyroid gland itself or lesions of the hypothalamic-pituitary system (e.g. pituitary adenoma). The majority of primary hypothyroidism is caused by autoimmune thyroiditis, radioactive iodine treatment or surgery. The clinical classification of hypothyroidism is generally based on the age at the onset of the thyroid gland. If hypothyroidism begins in the fetal or neonatal period, it is called cretinism; if it begins in pre-developmental childhood, it is called juvenile hypothyroidism (in severe cases, juvenile mucinous edema); if it begins in adulthood, it is called hypothyroidism (in severe cases, mucinous edema). Untreated hypothyroidism can lead to serious complications such as hypertension, hyperlipidemia, infertility, cognitive impairment and psychiatric disorders. Therefore, a timely and accurate clinical diagnosis of hypothyroidism is helpful for targeted treatment. The clinical symptoms of hypothyroidism are diverse and most of them rely on laboratory serological tests to confirm the diagnosis. The severity of hypothyroidism depends on the degree of thyroid dysfunction and the timing of the onset of hypothyroidism. Some of the specific symptoms of hypothyroidism include constipation, chills, dry skin, proximal muscle weakness, and thinning or loss of hair. However, most other clinical symptoms and signs are often non-specific, including weight gain, fatigue, lack of concentration, depression, muscle pain and menstrual disorders. Hypothyroidism is a common clinical condition, and early and timely diagnosis can help guide standardized treatment. The clinical manifestations of hypothyroidism are diverse and poorly specific, and the diagnosis is still mainly confirmed by laboratory serological tests (TSH, FT4, etc.). The normal value reference levels of these tests vary according to regional populations, and there is still a need to conduct large-scale epidemiological screening to obtain more accurate data. Future studies should focus more on specific types of hypothyroidism and related serious complications in order to improve the clinical treatment to improve the symptoms and quality of life of patients.