[Abstract] Deformation processes of Al nanopillars with different proportions of initial vacancies under the low amplitude cyclic load were simulated by molecular dynamics method. The paper aims to investigate mechanical behaviors of Al nanopillars with initial vacancies and its characteristics. According to the simulation results under cyclic load, the stress of the Al nanopillars at the stable state reached the maximum when the proportion of vacancies was 3%. When the proportion of vacancies was lower than 3 %, the number of dislocations in the process of nucleation and annihilation decreases greatly with the increase of vacancies. The stress of Al nanopillars at stable state became higher as increase of vacancies. When the proportion of vacancies was higher than 3 %, the number of dislocations in the process of nucleation and annihilation were not much difference in the different proportion of vacancies. The stress of Al nanopillars at stable state became lower as increase of vacancies.