The bonding interface of explosively-welded aluminium and steel in three explosive conditions have been investigated by using scanning electron microscopy, transmission electron microscopy, electron diffraction and electron probe microanalysis methods. The results show that all the interfaces have the shape of waves with curled front formed by process of superplasticity and some discontinuous reacted zones. They consist of amorphous and nano sized crystals and quasi-crystals as well as the compounds such as AlFe, Al2Fe, Al3Fe and Al6Fe with various shapes. The basal steel crystal near the interface has structure of martensite and perlite crystals which are deformed by the process of superplasticity. The size of reacted zone becomes large with increasing amount of explosive charge powder and separation of the driver Al plate from the basal steel plate.