There are six major features: ① prevalence in blood donors in high HBV prevalence areas accounted for 7% to 19%; ② often overlapping infection with hepatitis C or chronic alcoholic liver damage, different periods of hepatitis B and C virus can interfere with each other, but also aggravate and accelerate the development of the disease. The amount of HBV DNA can often be less than 104copies/ml. while the liver tissue is still positive for HBsAg and HBcAg. The amount of cccDNA in hepatocytes is still high, and the active situation of HBV RNA reverse transcription is not worse than that of patients with major triplets. ④ Mostly due to the sequence variation of S gene in hepatitis B DNA, so that S protein is not expressed or cannot be detected due to conventional methods. Their HBsAg negativity is undetectable using the general ELASE method. ⑤ In the hepatocytes HBsAg replication defective, but HBV DNA in monocytes in the extrahepatic replication is still very active. ⑥Positive HBV antigen antibody complexes can often be detected in the blood. There are four dangers of occult hepatitis B: ① patients with this type of hepatitis can infect recipients through blood transfusion, hemodialysis, and organ transplantation: ② hepatocellular carcinoma can still occur in these patients; ③ immune liver disease and hepatitis B nephropathy can develop; ④ mixed infections with hepatitis C can often affect the antiviral efficacy of interferon in patients with hepatitis C. To explore the situation of chronic hepatitis B in Chinese after HBsAg seroconversion, Hong Kong 2004 (Hepatology 2004, 39: 1694-1701) reported 92 cases of HBsAg seroclearance followed for 126 months and found that: 98% of patients had persistently undetectable HBV DNA in serum, but intrahepatocellular Low titer positive HBV DNA was present in 37% of patients and 71% to 100% in the form of cccDNA. Although their biochemical, viral and histological parameters were stable and HBV DNA quantification showed a gradual decrease, HCC could still occur with age. 92 cases in the HBsAg transversion group had 5 cases (5.4%) of HCC; 92 cases in the HBsAg non-transversion group had 8 cases (8.7%) of HCC in the same period. it is evident that occult hepatitis B did not reduce the incidence of hepatocellular carcinoma.