Abstract: To investigate the influence of gradient structure on the strength and plasticity of magnesium alloy, the magnesium alloy AZ31 with a grain gradient structure was fabricated by the surface mechanical rolling technique(SMRT).The gradient layer of the fabricated magnesium alloy has an approximate thickness of 900 μm, with grain sizes ranging from 3.5 μm to 120 μm, and the gradient layer constitutes about 20% of the total area. Uniaxial tensile and compressive loading tests demonstrate that the strength and ductility of the graded magnesium alloy are significantly enhanced compared to the original magnesium alloy AZ31. Microstructural analysis indicates that grain refinement and the presence of residual twins at the interface between coarse and fine grains effectively hinder dislocation movement, thereby contributing to the material's increased strength. Following tensile and compressive testing, it is observed that larger grains tend to generate a greater number of twins, whereas the smaller edge grains require higher stress levels for twinning deformation, resulting in minimal twin formation. This phenomenon is a key factor contributing to the observed increase in strength. The tensile fracture surface presents a tough fracture morphology, and the dimples show a gradient distribution. The diameter of the dimples gradually increases with the depth. The compressive fracture surface presents a cleavage fracture morphology, and the fine grains in the gradient layer inhibit the initiation and propagation of cracks, which is beneficial to the toughness improvement of the gradient structure magnesium alloy.