In order to investigate the behaviour of H2 molecules on Fe surface, the interaction between Fe and H atoms was characterized by molecular dynamics using the Reactive Force Field (ReaxFF) in atomistic simulations. The impact of environmental hydrogen pressure on H2 adsorption and H atom absorption on Fe(100) surface is researched at different temperatures. The analysis is done with variant methods to explore the relationship among binding energy, bond lengths, charge transfer and bond breaking under variant hydrogen pressures and temperatures.