<p>This study prepared 9Ni steel/S30408 composite plates through a multi-pass variable temperature rolling process with a reduction ratio gradient design, and systematically investigated the influence of rolling parameters on the interfacial bonding behavior and mechanical properties. The results showed that after two rolling passes, the interfacial bond strength and tensile strength exhibited non-monotonic changes. Microstructural analysis revealed that, compared with the first pass, the overall mechanical properties of the composite plate were improved after the second-pass rolling due to the synergistic effects of dislocation density gradient enhancement and grain refinement strengthening. However, the overall ductility decreased due to a decrease in interface bonding strength and a change in the Schmidt factor distribution. Reasonable allocation of the reduction ratio parameter was found to balance the Schmidt factor distribution and the difference in the dislocation density of the matrix, as well as regulate the interface bonding strength, thereby optimizing the deformation compatibility on both sides of the interface. The combination of a first-pass reduction rate of 34.6% and a second-pass reduction rate of 29% achieved optimal mechanical properties through coordinated deformation. Under these conditions, the interface shear strength was 472.15&#xa0;MPa; the ultimate tensile strength and fracture elongation were 806.90&#xa0;MPa and 29.68%, respectively. The two metals fractured simultaneously without interfacial cracking. This study provided a theoretical basis for the design of multi-pass rolling processes for dissimilar metal composite plates.</p>