Joining process and wavy interface formation behavior in explosive welded Cu/Al joints were investigated both numerically and experimentally. First, detonation of the explosive was simulated by Euler-Lagrange coupling method. Change in impact velocity and impact angle at the collision point during detonation was examined using a series of gauge points. Secondly, the numerical analysis of wavy interface formation was performed by using Smoothed Particle Hydrodynamics (SPH) method under the obtained impact velocity and impact angle conditions. The metal jet emission and wavy interface formation were clearly reproduced by the simulation. The Cu/Al lap joints were also fabricated by the explosive welding under the same condition. Microstructure observation revealed that the wavy interface including the intermediate phase layer was formed. The simulation results (wave amplitude and wave length) showed a good quantitatively agreement with the experimental results.