Covalently closed circular(ccc)DNA of hepatitis B virus(HBV)existed in the nuclei of HBV infected hepatocytes with a half-life time of 14.3 years in a mathmatic model.Viral protein feedback regulation in HBV life cycle to maintain vital viral replication is an important mechanism.Interleukin-6,epithelial growth factor,heme oxygenase-1,histones,and hepatocyte nuclear factors are demonstrated as the key regulators for HBV life cycle.CpG island structure and methylation status are involved in the regulation of HBV DNA replication.Nucleos(t)ide analogues are widely used in the clinical practice for the treatment of chronic hepatitis B patients,although no evidence indicating a direct inhibiton of HBV cccDNA.In the future,along with the study of HBV life cycle,new drugs including RNA interference technique,will pave the way to eliminate the HBV cccDNA from infected hepatocytes resulting final cure of chronic hepatitis B. Covalently closed circular (ccc) DNA of hepatitis B virus (HBV) existed in the nuclei of HBV infected hepatocytes with a half-life time of 14.3 years in a mathmatic model. Viral protein feedback regulation in HBV life cycle to maintain vital viral replication is an important mechanism.Interleukin-6, epithelial growth factor, heme oxygenase-1, histones, and hepatocyte nuclear factors are displayed as the key regulators for HBV life cycle. CpG island structure and methylation status are involved in the regulation of HBV DNA replication. Nucleos (t) ide analogues are widely used in the clinical practice for the treatment of chronic hepatitis B patients, although no evidence indicating a direct inhibiton of HBV cccDNA. The future, along with the study of HBV life cycle, new drugs including RNA interference technique, will pave the way to eliminate the HBV cccDNA from infected hepatocytes that will result in the final cure of chronic hepatitis B