Abstract: Three pairs of steel plate slabs with same composition and condition were bonded together under 5%, 10% and 15% first pass rolling reduction ratios respectively by vacuum rolling clad method. The microstructures and Z-direction mechanical properties of clad plate interfaces were investigated. The results showed that the size of the interface resultants becomes smaller gradually, and the amount of the resultants decreases with the increase of the first pass rolling reduction ratios, and the shape of the resultants distributed on the interfaces transforms from long stripe-like to fine grain. While the first pass reduction ratio reaches 15%, the interface is very clean. Furthermore, the Z-direction tensile stress, the elongation, the reduction of area and the plasticity are improved gradually with the increase of the first pass reduction ratio.