Liver is the largest organ of human internal organs, adult liver weighs about 1.5 kilograms, is the largest digestive gland of the digestive system, the liver has a complex function of synthesis, decomposition, transformation, detoxification, excretion, hormone degradation and so on. It is involved in the metabolism of sugar, fat and protein in the human body, the synthesis and balance of hemorrhagic and coagulant substances, the metabolism of bile acids, the conversion and excretion of bilirubin, and the process of energy reserve and energy supply. The liver receives blood supply from the hepatic artery and portal vein, and is a large blood bank in the human body. The liver has a strong regenerative capacity, which should be fully recognized and utilized in the treatment of various liver diseases. Specific functions are described as follows: (1) Participate in protein, sugar and fat metabolism: the liver is an important organ for the three major metabolism. It takes in the amino acids produced through digestion, absorption, and decomposition in the body and synthesizes proteins. All plasma albumin and part of alpha and beta globulin are synthesized in the liver. The liver can also convert non-amino acid substances into protein, which plays an important role in maintaining the balance of protein metabolism in the body. Liver dysfunction can cause a decrease in plasma albumin concentration and changes in the proportion of protein components. Sugar is an important substance for energy supply in the body, and the liver can decompose and synthesize hepatic glycogen and glycogen isomerization (converting non-sugar substances into sugar). When blood sugar rises after a meal, the liver can rapidly synthesize glucose into hepatic glycogen for storage. When hungry, hepatic glycogen can be broken down into glucose and fed into the blood circulation for the needs of the tissues. Therefore, under the regulation of neurological and endocrine factors, the liver plays a role in maintaining the stability of blood glucose. When liver function is impaired, decreased glucose tolerance can occur. In fat metabolism, bile secreted by the liver assists in the digestion and absorption of fat. At the same time, the liver is the hub for synthesizing, storing, decomposing and operating lipids. The liver synthesizes cholesterol, cholesteryl esters, phospholipids, endogenous triglycerides, and apolipoproteins, and is the only place where cholesterol is broken down. Cholesterol is broken down and excreted by bile. With hepatocellular injury, plasma cholesterol can be lowered; with biliary obstruction, plasma cholesterol is elevated. (2) Bilirubin metabolism: Hepatocytes have the function of taking up unconjugated bilirubin from plasma, conjugating it with glucuronic acid to conjugated bilirubin in hepatocytes, and excreting it into the biliary tract. Jaundice occurs when blood bilirubin levels rise as a result of hepatocellular injury or biliary tract obstruction. Bilirubin and its metabolites in blood, urine and stool can be used as test indicators. (3) Bile acid metabolism: cholesterol first forms primary bile acids in the liver and then becomes bound bile acids, which are excreted into the intestines and then absorbed by the small intestine and reintroduced to the liver, forming a hepatic-intestinal cycle. Therefore, liver and bile acid metabolism are closely related. Liver disease can cause an increase in the concentration of bile acids in the blood. (4) Bioconversion and excretion function: the liver can detoxify some endogenous or exogenous substances, such as various metabolites, foreign substances, various drugs or poisons through bioconversion and make them easy to be excreted out of the body with bile or urine. There are many substances excreted through the liver, such as cholesterol, bile acids, alkaline phosphatase and other normal components and some detoxification products. When hepatic excretory function is impaired, the body can be poisoned due to the accumulation of drugs or poisons. (5) Blood coagulation function: most of the coagulation and fibrinolytic factors are manufactured in the liver. Therefore, liver is very important to maintain the balance of coagulation and anticoagulation system. Bleeding tendency can be due to coagulation factor deficiency in liver disease. Liver function is very complex, in addition to the above, in vitamin metabolism, hormone metabolism, regulation of the body’s water, electrolyte balance and immunity also has an important role.