In the process of composite deformation for dissimilar metals, due to the different in metal properties and the asynchronous plastic deformation, it is easy to produce the void defects at the interface area, and the formation and evolution of void defects have an extremely adverse effect on the bimetallic interfacial bonding. Therefore, the development and evolution laws of voids in the deformation process for stainless steel/carbon steel composite rib under different tension coefficients were simulated by the finite element simulation technology. The results show that in the four passes with three-roll “tangent” feature, the metal in the roll gap area is in free deformation, and the cladding metal warps at the initial stage of deformation. At this time, the core metal has a small width, and the voids and voids are gradually formed at the interface. Moreover, the micro-tension rolling promotes the voids to expand further in the second pass, and the micro-tension improves the uniformity of wall thickness for the cladding metal. In the third and fourth passes of finishing, the voids gradually shrink and disappear, and the rolling process is successfully completed. The micro-morphologies of composite interface show that with the increasing of rolling temperature, the interface oxides are gradually decomposed, and the voids in the interface layer disappear. When the rolling temperature reaches 1200 ℃, the interface depth difference is only 3 μm, and the composite effect is better.