The influences of β2 phase volume fractions (PVF) and cryogenic temperatures on nanomechanical properties of Al-Mg-Si alloys were simulated by molecular dynamics. The simulation results show that when the β2 PVF is 0.107 at 77 K, the peak stress of Al-Mg-Si alloy is increased by 97.05% compared to that of pure aluminum. When the β2 PVF is 0.107, the peak stress of the sample at 27 K is increased by up to 23.55% compared to peak stress of sample at 300 K. Cryogenic environments help to enhance total dislocation density, allowing samples to withstand greater stress, which can provide additional strength and ductility. Temperature decrease can also appreciably inhibit the initiation and growth of voids (growth rate is decreased by 88.5% at 27 K), which contributes to the enhanced ductility.