HIV belongs to the group of human immunodeficiency viruses in the genus Lentivirus in the family Retroviridae in the classification of viruses. There are 4 reasons for its high genetic variability as follows 1, high error rate of the reverse transcriptase, replication can not be timely excision of the wrongly introduced nucleotides, about one error in each replication cycle will occur to make the virus replication when the random mutation. 2, the rapid replication of the virus, about every day an HIV-infected person to produce and remove 10 billion viral particles. 3, host immune selection, under the action of host immune pressure, so that the genome can stimulate the host cellular or humoral immunity of the variation higher than other parts, such as gp120 V3 ring high variation region. 4. Genetic recombination between DNA of different viral strains. The full length of HIV gene is about 9.8kb, containing 3 structural genes, gag, pol, env, 2 regulatory genes (tat trans-activator, rev virulence particle protein expression regulator) and 4 auxiliary genes (nef negative regulator, vpr viral r protein, vpu viral u protein and vif virulence particle infectivity factor). HIV is a highly variable virus, with varying degrees of variation in each gene and the highest rate of variation in the env gene. HIV prevalent worldwide so far can be divided into two types, HIV-1 and HIV-2, based on serological response and viral nucleic acid sequence determination. Between HIV-1 and HIV-2, only 40-60% of the nucleotide sequences are homologous. Within HIV-1, the genetic dispersion rate among subtypes is 20%-35%, and the genetic dispersion rate within the same subtype is 7%-20%. HIV-1 is currently prevalent worldwide. Based on the homology of the sequence of the env gene encoding the envelope protein and the gag gene encoding the capsid protein, HIV-1 is further divided into three groups, M (main), O (outline) and N (new, or non-M, non-O new or non-M non-O group), of which M has so far There are 11 subtypes A, B, C, D, E, F, G, H, I, J, and K. Group O was isolated from Cameroon and Gabon in 1990 and has only 50% amino acid sequence homology with the other subtypes of group M. Group N was isolated only recently from two Cameroonian patients and is a new group of viruses that belongs neither to group M nor to group O in the phylogenetic tree, so it is called group N. The biological characteristics of HIV-2 are very similar to those of HIV-1, but it is less infectious and causes a slower clinical progression of AIDS and milder symptoms. HIV-2 has at least 7 subtypes A, B, C, D, E, F, and G so far. In China, HIV-1 is the main prevalent strain, and there are 8 subtypes of A, B (European and American B), B’ (Thai B), C, D, E, F and G. There are also different prevalent recombinant types, and a few HIV-2 infections have been found in some areas since 1999. However, no reports of O and N types have been found so far. Early detection and identification of various subtypes of HIV is important for epidemiological investigation, timely diagnosis, development of new diagnostic reagents, new drug development, and vaccine development and research.