Series of multilayer TWIP/TRIP steels were hot rolled at 1000 degrees C with different rolling reduction ratios of 25%, 50%, 60%, 70%, 80%, 90% and 94%, and some in-situ reacted Al2O3 whiskers were identified at the clad interface based on selection oxidation. The continuous oxidized films or walls were broken and separated into fine dispersed reinforcements with increasing rolling reduction ratio, which are beneficial to strengthen the interface and toughen the multilayer steels. At low rolling reduction ratio, the thick oxidation walls inhibit the grain growth and alloy element diffusion, leading to the weakness of interface bonding and interface delamination. However, at high rolling reduction ratio, the fine dispersed Al2O3 whiskers bridge the clad interface and induce grain crossing, resulting into strong interfaces and high uniform plastic deformation capacity. Moreover, the grain crossing phenomenon and inner TWIP/TRIP coordination deformation mechanism provide a novel approach for improving fracture elongation of multilayer steels.