Hepatitis B DNA should refer to hepatitis B virus DNA. Hepatitis B virus DNA is an indicator to determine the infectiousness of hepatitis B virus by detecting the level of hepatitis B virus in blood, and is one of the examination items for chronic viral hepatitis B. Hepatitis B virus DNA is a genetic material of hepatitis B virus, which is the core material of hepatitis B virus and the basis of virus replication, and is the most direct, specific and highly sensitive reliable quantitative indicator of HBV infection. Positive hepatitis B virus DNA indicates the presence of hepatitis B virus replication in the patient’s body, and the higher the level, the stronger the virus replication and the greater the infectiousness. For example, for HBeAg-positive patients with chronic hepatitis B, when the DNA of hepatitis B virus in their serum is >1x10E5copies/ml and the transaminases are elevated more than twice the normal value for 3 months, it indicates that the hepatitis B virus is actively replicating and the amount of virus in the body is high, so antiviral treatment should be started immediately. If the hepatitis B virus DNA turns negative to positive during treatment, it indicates that viral resistance has occurred and other antiviral drugs need to be added or changed. Hepatitis B virus DNA testing is reported in two main ways: qualitative, which determines whether the test is negative or positive, and quantitative, which detects the amount of hepatitis B virus in the blood. Viral load testing can provide important clinical information about the need for treatment, but must be combined with other test results to determine together, as hepatitis B virus is a tricky virus to take seriously.