Abstract: Electromagnetic Pulse Welding (EMPW) technology is widely concerned because of the reliable connection of dissimilar metals driven by high-voltage discharge. However, the interface bonding mechanism is still unclear. A comprehensive experimental platform for copper-aluminum EMPW is set up, the welding dynamic process is captured, and the collision velocity and angle are obtained. Based on these parameters, a molecular dynamics simulation model is constructed for the formation of typical interfaces (flat interface and vortex interface) in EMPW. The atomic diffusion behavior in the welding process is studied, and the thickness of the diffusion layer at the typical interface is calculated. The microstructure of the bonding interface is analyzed by the transmission electron microscopy. The research results show that the severe collision drives the plastic deformation of the interface material, which forms metallurgical bonding and mechanical engagement. This is the bonding mechanism of the copper aluminum EMPW interface. And the atomic diffusion thickness at the vortex interface is greater than that at the flat interface. This paper can provide a scientific basis for further understanding the mechanism of EMPW and regulating the welding effect.