A mathematic model has been built to describe the cladding casting process and the casting parametric influence on the cladding billet. The effect of casting speed, casting temperature and internal cooling water rate on the casting process performance was discussed. Based on the numerical simulation results, the cladding billet was prepared successfully. Moreover, the model has been verified against the temperature measurements during the cladding casting process. The interfacial characteristics were investigated using metallographic examination, Energy Dispersive Spectrometer and universal testing machine. The results show that there is a good agreement between the measured and calculated results. The comprehensively considered casting process is: casting speed is 100mm/min, internal cooling water rate is 35L/min, casting temperature are 1020K (AA4045) and 1000K (AA3003). Based on the simulation results, the AA4045/AA3003 cladding billet with no defects in size of φ140/φ110mm was fabricated successfully. A diffusion layer in width of 15 μm formed around the bonding interface. The interfacial bonding strength is 107.3MPa, higher than that of AA3003, indicating that the two alloys have bonded metallurgically.