There are three basic conditions for the spread of AIDS, namely, the source of infection, the means of transmission and the susceptible population. 1. Source of infection: People who are carrying HIV and have AIDS themselves are the only source of infection, and there are some seropositive HIV carriers who do not have any other symptoms, which also take up a large proportion of the transmission. 2. Transmission: The main modes of transmission of AIDS are blood transmission, sexual contact transmission and mother-to-child transmission. Other body fluids, such as blood, semen, vaginal secretions, breast milk, prostate fluid and other body fluids with extremely high viral content, can lead to the spread of the virus. 3. Susceptible groups: Generally speaking, men who have sex with men, intravenous drug dependents, sexual promiscuity, and people who have received multiple blood transfusions or blood products are high-risk groups. Daily attention should be paid to the protection of AIDS, avoid high-risk behaviors, if there is a high risk of HIV infection, timely specialist consultation.