With the continuous improvement of people’s living standards, fatty liver is gradually increasing in China, and in recent years there has been a rapid increase in the trend, and has become one of the important pre-cirrhotic lesions of liver fibrosis and cirrhosis. Normal people contain about 4-5 grams of lipids per 100 grams of liver wet weight, of which phospholipids account for more than 50%, triglycerides account for 20%, free fatty acids account for 20%, cholesterol about 7%, and the rest are cholesteryl esters. When the accumulation of lipids in hepatocytes exceeds 5% of the wet weight of the liver, or when more than 1/3 of the hepatocytes are histologically lipidic per unit area, it is called “fatty liver”. According to the fat content of the liver, fatty liver can be divided into three degrees: mild (containing 5-10% fat), moderate (containing 10-25% fat) and severe (almost all hepatocytes are fatty). The fatty liver is also divided into three stages according to whether the liver tissue is accompanied by inflammation: stage I is “simple fatty liver” without inflammation; stage II is “steatohepatitis” with inflammation and fibrosis in the confluent area; stage III is complete fibrosis and pseudobulbar formation. That is, “fatty cirrhosis”. The diagnosis of “fatty liver” can be made when the amount of fat stored in the liver accounts for more than 5% of the liver weight or when the histological manifestation is more than 30-50% of hepatocellular steatosis. However, in clinical practice, the diagnosis cannot be made by liver tissue biopsy, and the blood biochemical indexes are not consistent with the degree of fatty liver lesion, so ultrasound, CT, MRI and other imaging tests have become very important and practical clinical diagnostic tools. (1) Ultrasound examination: Diffuse fatty liver has its unique performance on ultrasound images, with hyperechoic spots, which some people call “bright liver”. Ultrasound can detect fatty liver with liver fat content of 30% or more, and fatty liver with liver fat content of 50% or more, and the sensitivity of ultrasound diagnosis can reach 90%. (2) CT: The CT value is significantly negatively correlated with the amount of liver fat deposition, and the ratio of liver/spleen CT value can be used as a reference standard to measure the degree of fatty liver because the CT value of the spleen is often fixed. CT is superior to B ultrasound in the diagnosis of fatty liver, and its accuracy is better than that of B ultrasound, but its cost and radioactivity are its shortcomings. (3) Magnetic resonance imaging (MRI): MRI and hepatic arteriography are mainly used for those who have difficulty in diagnosis by ultrasound and CT, especially when it is difficult to differentiate focal fatty liver from liver tumor.