AIDS is characterized by the replication of the virus in the body after infection with AIDS. As the virus continues to increase, it will continue to attack the body’s immune system, mainly CD4+ T lymphocytes, thus causing a continuous decline in CD4+ T lymphocytes. After the CD4+ T-lymphocyte count drops to a certain level, the patient will develop an opportunistic infection, usually <200/mm^3, and the patient will be prone to the AIDS stage. During the AIDS stage patients can develop various opportunistic infections in various systems due to the collapse of the immune system, such as Pneumocystis pneumonia, Cryptococcal meningitis, and also malignant lymphoma, Kaposi's sarcoma, etc. If left untreated, patients will eventually die due to opportunistic infections as well as malignant tumors.