Abstract: Reactive force field model (ReaxFF) molecular dynamics simulation was performed to study the stability of supported-atom (or ad-atom) modellabeled as M₁/Cu(111), M=Pt, Ni, Ag, Fe and the embedded (or doped) modelsnoted as M₁@/Cu(111) systems. For the M₁@/Cu(111) catalyst models, it was found that the Pt(Ni, Fe)₁@/Cu(111) is more stable compared to Ag₁@/Cu(111) model (temperature>500 K). For supported-atom models, except for Fe₁/Cu(111) none of them can exist stably at 100~500 K. And these single metal atoms migrate to each other and then aggregate to form large nanoparticles besides Fe atoms diffusing to subsurface as temperature increases. In addition, the effect of H₂ and O₂ atmosphere on the surface of single atom alloy(SAA) catalyst model and thermal stability was invesgated by the optimized Cu/Pt/C/H/O force field parameter. It was found that the presence of H₂ reduces the stability of M₁@Cu(111) catalysts. The simulation results show that M₁/Cu(111) of SAA are not good candidates for catalysts even at relatively low temperature while most M₁@Cu(111) models can exist stable over high reaction temperature.