By using the molecular dynamics method, the effects of two different grain sizes and strain rates on the mechanical properties of the FeNix/Fe alloy models were investigated with four different Ni contents, and the mechanical behavior of the alloy under cyclic tensile loading has also been explored. Calculated results show that the average grain size increases from 2.34 to 7.12 nm, and the elastic modulus increases. These models were tensile at two different strain rates, and it exhibited higher yield strength at higher strain rates. In different Ni contents models, when subjected to cyclic tensile and compressive loading, the Ni content changes the stress amplitude of the alloys during cycling. The stress-strain curves of the FeNi26/Fe and FeNi43/Fe alloy models, which show a more erratic curve morphology with the increase in the number of cycles, are related to the addition of Ni as an alloying element.