The probability of HIV infection should be analyzed on a case-by-case basis. The main ways of HIV transmission are blood transmission, vertical transmission from mother to child, and sexual transmission, and the infection rate ranges from 0.3% to 80%. 1. Blood transmission: If blood transmission is involved and it is determined that the blood contains HIV, the probability of infection is about 50% to 80%. In case of occupational exposure in clinical work, the infection rate is around 0.3%. 2. Vertical transmission: generally mother-to-child vertical transmission. The probability of infection is 20%~60% if mother-to-child vertical transmission is treated with blocking drugs, which can reduce the possibility of transmission. 3. Sexual transmission: In a single unprotected heterosexual act, the probability of male-to-female transmission is generally 0.08%, and the probability of female-to-male transmission is generally 0.04%. The risk of transmission is greatest between same-sex behaviors, such as gay men, and the probability of infection is about 1% to 2% for anal sex if mucosal damage occurs. Daily life contact, such as shaking hands, hugging, eating, office work, etc., these behaviors do not cause HIV infection.