Abstract: Pointing to the diffusion behavior of atom and the law of phase transition in metal interface for stainless steel and carbon steel, a further research is of great significance for improving the quality of metallurgical bonding and realizing the property regulation of product. In this paper, based on the kind of material calculation method of molecular dynamics, cell models including carbon steel body-centered cubic (BCC)-Fe and stainless steel face-centered cubic (FCC)-Fe were established apart under COMPASS force field. And the system of constant temperature and volume (NVT) and the system of constant temperature and pressure (NPT) were also employed in the two different stages of high-temperature insulation with the temperature of 1423 K and continuous compression with the stress of 2 GPa and 4 GPa, respectively. On this base, the change behavior of non-congruent metal interface was simulated through the indicators of interfacial microstructure, the mean-squared displacement distribution, the radial displacement function and the interface elemental distribution. The results show that the phase transition of BCC-Fe→FCC-Fe happens to occur in the carbon steel side during the high-temperature insulation stage, accompanying the space transition of P1→FM-3M in a disordered and long-range diffusion process. During the loading relaxation stage of 200 ps, the boundary atoms are embedded in each other until the interface forms a unified FCC crystal. With the increase of pressure, the interface structure produces a large number of slips and misalignments along the most densely-rowed crystal face of (111), and the two groups of atoms could success an effective diffusion and migration.