Objective To observe the process of SIVmac239 adsorbing onto and infecting target cell line CEMx174 and revealing the basis for the virus entering target cells. Methods CEMx174 cells were infected by the SIVmac239 virus. Culture supernatants and cells were collected at various time points. The viral load in culture supernatants was detected by quantitative real?time PCR. Expression of intracellular viral protein p27 was detected by indirect immunofluorescence, intracellular staining, and Western blotting. Results CEMx174 cells absorbed the virus and were infected. Virus particles were detected on the cell membrane at 0.5 h. At 12 h, the level of viral RNA in the culture supernatant was reduced. Then up to 96 h, the expression of SIV p27 in the cytoplasm was increased, and the level of viral RNA in the culture supernatants increased continually. Conclusions When the virus infects its target cells, it is first adsorbed through virus?associated receptors and then enters the cell.