Molecular dynamics simulations are employed to simulate the axial compression of both perfect and defective armchair single-walled carbon nanotubes (SWCNTs). Three temperature conditions are considered. It is revealed that the vacancy defects in SWCNTs have remarkable influences on their buckling properties, especially at low temperature. It is noticed that the single vacancy defect leads to excessive stress concentration, as a result of which the local buckling occurs easily at the defective position. Thus, the (7, 7) tube with single vacancies seems inferior to that with double vacancies.