Abstract: With the help of molecular dynamics material calculation methods, in-depth investigation of the structural evolution of the composite interface and the diffusion of atomic thermal motion is of great significance for improving the quality of intermetallic metallurgical bonding and realizing the regulation of product performance. In this paper, the molecular dynamics simulation software Materials Studio was used to construct the cell models of stainless steel FCC-Fe and carbon steel BCC-Fe based on the COMPASS force field under complex stress conditions; the NVT ensemble was used to simulate the structural evolution of noncoherent composite interfaces at a high temperature of 1423 K; and the NPT ensemble was used to compare the interface slip and atomic thermal motion migration behavior under the complex conditions of 'three-dimensional compressive stress' and 'two-pressure and one-tensile stress'. The results show that in the NVT relaxation stage, the BCC crystals on the carbon steel side are transformed into FCC crystals under the influence of the high temperature effect, while the FCC-Fe crystals on the stainless steel side are strengthened by the solid solution of Cr and Ni elements, and the crystal structure does not change, and at this time, there exists an obvious interface between carbon steel and stainless steel. In the NPT relaxation stage, by the "three-way compressive stress", the composite interface produces sporadic diffusion. There is a certain amount of residual stress in the interface, resulting in atomic disorder and misalignment of grain boundaries. Under the condition of “two presses and one pull”, the tensile stress can release the stress between grain boundaries, and the interface between stainless steel and carbon steel has a tendency of continuous slip, and the two sides of the FCC crystals have the same orientation, which helps the atoms on both sides to be embedded in each other, and there is no obvious distinction between the grain boundaries. In addition, the radial distribution functions, atomic velocity fields, and elemental diffusion on both sides of the interface likewise indicate that lateral tensile stresses are favorable to improve the interfacial crystal fusion, and the misaligned band atoms have enough energy to cross the potential barriers to form slips and improve the interfacial bonding strength. The results of the microtension rolling test show that the composite interface is uniform and free of voids, and the transition of the elements of the composite layer is obvious. However, there are differences in metal deformation between the two sides of the interface. The grain refinement on the carbon steel side is uniform, and the subgranular organization with a high density of small-angle grain boundaries is segmented inside the grains and near the grain boundaries to form a dislocation network in low-energy states, which provides high-strength properties for the composites. The proportion of large-angle grain boundaries on the stainless steel side is as high as 73.76%, which plays an important role in preventing intergranular corrosion and crack propagation.