Brass-coated steel cords are widely used as reinforcement material for rubber composites. The adhesion between steel cord and rubber is critical throughout the lifetime use of steel cord/rubber composites; thus, the adhesion mechanism has been a focus of the rubber industry for several decades. Various modern analytical instruments, such as X-ray spectroscopy and mass spectroscopy, have been applied to the study of this bonding interface. In this paper, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) was used to research the morphology of the steel cord surface and the adhesion mechanism. According to these morphology testing results, the rubber residue bands were observed be orientated and located mostly in Cu/Zn void areas. Further research reveals that macro-structure adhesion layer leads to interlocking mechanism for rubber residue.