Non-alcoholic fatty liver disease (NAFLD), also known as non-alcoholic fatty liver, is a class of clinicopathologic syndromes in which the histologic changes of the liver resemble those of alcoholic liver disease, but there is no history of alcohol consumption. NAFLD includes three main types: non-alcoholic simple fatty liver, non-alcoholic steatohepatitis (NASH) and non-alcoholic steatohepatitis cirrhosis, of which NASH is an important intermediate stage in the progression of NAFLD.NASH has become one of the most important pre-cirrhotic lesions after chronic viral hepatitis and alcoholic liver disease, and is also one of the most important pre-cirrhotic lesions in clinical serology. NASH has become one of the most important pre-cirrhotic lesions after chronic viral hepatitis and alcoholic liver disease, and is also one of the common causes of clinical serum aminotransferase abnormalities. (A) Basic diagnosis Clinically found that patients with liver function impairment, suspected of non-alcoholic fatty liver disease, should pay attention to differentiate with the following diseases: with uniform fatty liver disease: 1, drug liver disease, with a history of taking liver damage drugs, no blood glucose and blood lipids increase, ultrasound without fatty liver characteristic changes 2, chronic viral hepatitis, with viral hepatitis markers are positive, need to pay attention to part of the patients in the viral hepatitis carriers combined with non-alcoholic fatty liver disease, and the combination of non-alcoholic fatty liver disease on the basis of chronic toxic hepatitis, and the combination of non-alcoholic fatty liver disease. Based on the combination of non-alcoholic fatty liver, often need to further check HBV-DNA, to determine the cause of liver function damage 3, autoimmune hepatitis check autoimmune indicators positive findings can be identified (see section IV of this chapter). 4.Early hepatomegaly Some patients with hepatomegaly may only show liver function impairment in the early stage, and serum copper and copper blue protein levels need to be tested. Inhomogeneous steatohepatopathy 1, cirrhotic nodules Imaging with typical cirrhotic changes can generally be distinguished, and some patients need histologic examination of the lesions for differentiation. 2.Primary hepatocellular carcinoma with increased AFP, when some patients are difficult to distinguish, it needs to be combined with CT, MRI, DSA and even histologic examination to be confirmed. Metastatic liver cancer with primary lesion changes, AFP is not elevated, but often accompanied with other positive tumor markers of the primary lesion, and typical CT examination has “bull’s eye sign”. Hepatic fibroma: patients have no underlying liver disease, good general condition, all tumor indicators are negative, CT, MRI can be differentiated, and histology is needed for differentiation when necessary. (B) clinical type of non-alcoholic fatty liver disease clinical diagnostic criteria: where the following items 1-5 and 6 or 7 can be diagnosed as non-alcoholic fatty liver disease: ① predisposing factors such as obesity, type 2 diabetes mellitus, hyperlipidaemia and women, etc. ② no history of alcohol consumption or weekly alcohol consumption.