Hepatitis B virus DNA is a method of detecting the hepatitis B virus using PCR technology and is a direct indicator of viral replication and infectivity, including both qualitative and quantitative. Qualitative: That is, it determines whether it is negative or positive, and its normal value is negative. A positive test indicates that the hepatitis B virus is replicating and is readily transmissible. A negative indicates that it is not readily transmissible. Quantitative: The level of hepatitis B virus in the blood is important for determining the degree of virus replication, the size of infectiousness, and the efficacy of antiviral drugs, but it is not directly related to the severity of the disease. The higher the level, the stronger the virus replication and the more infectious the HBVDNA test is, as well as the pre-C region variant, genotyping and genetic resistance variant sites. The pre-C region variation may be related to the occurrence of heavy hepatitis, genotyping has some significance for prognosis and the efficacy of antiviral drugs, while the detection of genetic resistance variants is important for nucleoside analogue antiviral therapy. Therefore, hepatitis B virus DNA is an important indicator for hepatitis B patients when they undergo examination or review, which is important for assessing viral replication and infectiousness, but also together with liver function, ultrasound and other indicators, so that the disease can be monitored in an integrated and comprehensive manner.