Abstract: The effects of different tensile directions (0001 and 11$\overline{2}$0 crystal directions) on the tensile properties and plastic deformation mechanism of single crystal magnesium at the temperature of 300 K and strain rate of 10⁹ s⁻¹ were studied by molecular dynamics simulation method. The results show that the tensile behavior of single crystal magnesium showed anisotropy. The elastic modulus, yield strength and potential energy barrier that plastic deformation needed to overcome along the 0001 crystal direction were large, and twice yield occurred; deformation was difficult in this direction. The mechanism of plastic deformation along 0001 crystal direction was that the first yield was dominated by the nucleation and growth of the 10$\overline{1}$2 tensile twin, and the second yield was dominated by the 10$\overline{1}$2-10$\overline{1}$1 secondary twin. The elastic modulus, yield strength and potential energy barrier that plastic deformation needed to overcome along the 11$\overline{2}$0 crystal direction were small, and there was only one yield; deformation was easy in this direction. The tensile plastic deformation mechanism along 11$\overline{2}$0 crystal direction was that the initial yield was dominated by the nucleation and growth of the 10$\overline{1}$1 compression twin, and then the local stress concentration at twin boundaries occurred under the interaction between dislocations and twin crystal in the crystal.