A positive hepatitis B surface antigen indicates infection with the hepatitis B virus. Hepatitis B surface antigen is the outer shell protein of the hepatitis B virus, which itself is only antigenic and not infectious. If the hepatitis B surface antigen is positive, it is necessary to further check the quantification of HBV-DNA of the hepatitis B virus. Based on the quantification of HBV-DNA, the current active status of the hepatitis B virus can be determined. If the viral replication is active and antiviral therapy is appropriate, antiviral drugs should be applied as soon as possible. Currently, the main antiviral drugs are interferon, entecavir and tenofovir. When applying interferon, it is important to monitor the side effects, mainly fever, flu-like syndrome and bone marrow suppression. When applying tenofovir, monitor renal function, as there are occasional side effects of nephrotoxicity.