Hepatitis B is a blood-borne disease, and hepatitis B virus (HBV) is mainly transmitted through blood and blood products, mother-to-child and sexual contact. Due to strict screening of blood donors for hepatitis B before donation, HBV infection caused by blood transfusion or blood products is now less common. The route of hepatitis B virus transmission varies significantly by age. In infants and young children, the infection is mainly due to perinatal vertical mother-to-child transmission, mostly through contact with the blood and body fluids of HBV-positive mothers during delivery. In childhood, transmission is mainly through contact with broken skin and mucous membranes of infected relatives in the family. In adolescence and adults, transmission is mainly through sexual transmission, occupational exposure and injection drug use. The use of medical devices, invasive diagnostic and surgical operations and procedures that are not strictly sterilized can make transmission possible for all ages. In addition, hepatitis B can also be transmitted through foot trimming, tattooing, ear piercing, accidental exposure during the work of medical personnel, and sharing razors and toothbrushes. It should be noted that HBV is not transmitted through the whistle and gastrointestinal tract, so daily work, school or living contacts, such as working in the same office, shaking hands, hugging, living in the same dormitory, eating in the same restaurant and communal toilets without blood exposure, generally do not transmit hepatitis B virus. Epidemiological and laboratory studies have also not found that HBV can be transmitted by blood-sucking insects (mosquitoes, bedbugs, etc.).