Explosive welding is a kind of solid state welding method, and a strong metallurgical bonding can be obtained with a wide range of metal combinations. Depending on metal combinations, an intermediate layer (IML) is formed at part of the joint interface by solidification of the local melting zone. When the excessive intermediate layer is formed along the joint interface, the bonding strength decreases drastically. Therefore, it is desirable that the intermediate layer is reduced at the joint interface. In order to control the formation of the intermediate layer at the joint interface, it is necessary to reveal the cooling process at the joint interface and formation process of the intermediate layer on the explosive welding. However, it is difficult to observe the phenomenon occurring at the joint interface of the explosive welded joint which is completed in a very short time, experimentally. In this study, the cooling process at the joint interface and formation process of IML were investigated by the simulation and experiment. The cooling rate at the local melting zone reached over 106K/s. This rapid cooling was caused by large temperature gradient between joint interface and base metals. The solidification of IML proceeds from the outside of the local melting region toward the center and the final solidification area of the IML becomes the central part of the local melting region. Therefore, it is considered that the void observed at the center of the IML at the actual bonding interface is due to the solidification shrinkage generated at the final solidification area. The wavy interface (wave height, wavelength) obtained by explosive welding and the composition of the IML and the position of the void were quantitatively in good agreement with the interface form obtained by numerical analysis.