In patients with chronic viral hepatitis B, if fever develops and lasts for a longer period of time, consideration should be given to whether the hepatitis B virus is in a replication phase. At this time, the patient should be further investigated for hepatitis B tri-system, hepatitis B DNA and liver function. If the virus is replicating and the liver function is impaired, the long-term liver function impairment will lead to a decrease in the liver’s detoxification ability and cause the accumulation of toxic substances in the body, which will also cause the patient to have prolonged fever. When a patient has acute or severe hepatitis, or cirrhosis, a peritoneal effusion may develop. Peritoneal effusion, if combined with infection, may also cause the possibility of fever in patients. In some patients, there is a possibility of bacteremia and sepsis, which can also cause fever. In addition, in patients with hepatitis B, chronic liver impairment due to long-term use of other drugs can also cause prolonged fever. If the patient has fever for a longer period of time, combined with elevated fetoprotein and other substances, the possibility of liver tumor cannot be ruled out. Generally, further ultrasound of the upper abdomen and enhanced CT of the upper abdomen are needed to further determine the nature of the disease.