Abstract: In order to produce diffusion-rolling sandwich panels under small reduction, a bonding assistant coat which mainly contains Cu, Zn, Mn and small amount of Si, Sn, Ni, B and rare earth elements was designed for carbon steel plates at 850℃. The results of SEM and rolling showed that atom diffusion between the carbon steel plate and the bonding assistant coat took place, the interface combination was satisfied and the thickness of bonding assistant coat accorded with small reduction later.