Hepatitis B, known as viral hepatitis B, is an infectious disease caused by hepatitis B virus infection, mainly liver lesions. The disease is prevalent throughout the world, and China is a high prevalence area. Hepatitis B is caused by hepatitis B virus infection, which can be transmitted through blood and blood products, close contact, especially sexual contact, mother-to-child vertical transmission and medical transmission, etc. Hepatitis B virus can trigger a series of immune responses after entering the body, thus triggering clinical symptoms of liver damage. Hepatitis B virus infection leads to various forms of liver damage or disease, including acute hepatitis, chronic hepatitis, asymptomatic carriers, various types of liver failure, cirrhosis and hepatocellular carcinoma. The clinical manifestations of hepatitis B depend on its clinical classification and severity, and most patients have symptoms of liver disease such as fatigue, loss of appetite, nausea and vomiting, anorexia of greasy food, pain and discomfort in the right upper abdomen, and liver function abnormalities. The severity and outcome of hepatitis B are influenced by many factors, such as the variability and replication level of the virus, the host’s immune function and the intensity and breadth of the nonspecific inflammatory response, as well as other comorbidities and other viral co-infections. Antiviral therapy is the key to the treatment of hepatitis B. Effective antiviral therapy can inhibit viral replication for a long period of time, reduce hepatocellular inflammation and necrosis and hepatic fibrosis, and delay and reduce the occurrence of hepatic impairment and its complications, thus improving the quality of life of hepatitis B patients and prolonging their lifespan. However, not all hepatitis B virus-infected patients need to receive antiviral treatment, only those with significant hepatitis flare-ups and the resulting high risk of cirrhosis and hepatocellular carcinoma in the patient’s future need immediate treatment. To summarize, hepatitis B is an infectious disease with predominantly liver lesions caused by immune damage triggered by human infection with the hepatitis B virus.