Abstract: Due to the excellent mechanical properties of gradient nano-grained structure, the microstructure evolution process under tensile strain is studied by using phase-field-crystal model. The results show that in gradient nano-grained structure, the deformation of coarse grains is mainly through dislocation slip, while the deformation of fine grains is mainly through grain boundary migration. The gradient nano-grained structure inhibits dislocation and grain boundary migration, and the inhibition effect is enhanced with the increase of grain size gradient. Therefore, the yield strength increases with the grain size gradient. Meanwhile, the uneven stress distribution of the gradient nanocrystalline structure helps to overcome the resistance caused by the high dislocation density in the fine grain region and promote the dislocation movement to produce plastic deformation, so that the overall plastic deformation ability is not weakened. The deformation mechanism and mechanical properties of gradient nano-grained structure are proved theoretically, which provides a reference for the research in related fields.