<p>The manuscript presents a new manufacturing technology for fabricating bimetallic hollow shafts. Cross-wedge rolling (CWR) bimetallic hollow shafts with mandrels increase hole quality by controlling bore shape and decreasing internal flaws. It also increases the quality of the interface combination. In this study, the interfacial bonding quality and deformation laws are investigated by finite element and experimental with different the relative mandrel diameter. The stress–strain field, metal flow, temperature, and rolling force of the workpiece were analyzed in detail by finite elements. The stress in the deformation zone of the interface is three-way compressive stress, and the radial stress is the most advantageous to the interface welding. Along the direction of thickness, the interfacial stress–strain gradient is observed. As the relative mandrel diameter increases, the maximum outer diameter size of the rolled part increases and the non-circularity increases, and the shear strength increases first and then decreases. The microhardness of interface accessories slightly increases with the increase of mandrel diameter, and peaks and valleys appear on the right and left sides of the interface. According to the results of microstructure, the increase of the diameter of the mandrel is conducive to the improvement of the microhardness and the interface strength, and the grains on both sides of the interface were significantly refined with increasing the relative mandrel diameter. The study’s findings can provide theoretical guidance for the fabrication of the CWR bimetallic hollow shafts.</p>