HBV is a hepatophilic DNA virus with a genome length of about 3.2 kb and is partly double-stranded cyclic DNA. HBV is resistant, but HBV can be inactivated by boiling at 65°C for 10 h, boiling for 10 min or high-pressure steam. ethylene oxide, glutaraldehyde, peroxyacetic acid and iodoform also have good inactivation effects on HBV. After HBV invades hepatocytes, part of the double-stranded cyclic HBV DNA is used in the nucleus to extend the positive chain with negative-stranded DNA as a template to repair the cleft area in the positive chain, forming covalent closed-loop DNA (cccDNA); then cccDNA is used as a template to transcribe into several mRNAs of different lengths, which are used as pregenomic RNA and encode various antigens of HBV. (The cccDNA has a long half-life and is difficult to completely remove from the body. HBV has been found to have 9 genotypes, A-I, with C and B types predominating in China. HBV genotype is associated with disease progression and the effectiveness of interferon alpha therapy. Compared with those infected with C genotype, those infected with B genotype showed HBeAg serological conversion earlier and progressed less to chronic hepatitis, cirrhosis and primary hepatocellular carcinoma.