In order to reveal the diffusion behavior of Ti/Al interface, the molecular dynamics simulation was applied to study the microscopic diffusion mechanisms of Ti/Al explosive welding interface at the atomic scale. Molecular dynamics model of Ti/Al explosive welding spot was established by Materials Studio (MS). According to the physical process of explosive welding, the simulation of the collision was divided into two stages: the loading stage and the unloading stage. The mean square displacement (MSD), radial distribution function (RDF), and diffusion layer thickness were calculated by LAMMPS, and the diffusion behavior of interfacial atoms at different stages was reproduced by OVITO. Results show that in the loading stage of explosive welding, Ti and Al atoms do not diffuse but only vibrate at the equilibrium position, and the vibration of Al atoms is stronger than that of Ti atoms. The atomic diffusion only occurs in the unloading stage of the explosive welding process. The Ti-Ti bonding energy is too high to break. The Al-Al bonding energy is low, so it is easy to be damaged, resulting in vacancies, gaps and other defects, which promotes the deep diffusion of Ti atoms into the Al substrate lattice while hindering Al atoms from entering the Ti substrate lattice. The simulation result is basically in accordance with EDS experimental result.