The invention discloses a metallurgical bonding double-metal stainless steel cladding reinforcing steel bar and a preparation process thereof. The metallurgical bonding double-metal stainless steel cladding reinforcing steel bar comprises a carbon steel core part and a stainless steel cladding. The composite forming process comprises the following steps: integrally heating an outer-layer stainless steel pipe to 600 to 1000 DEG C by using an induction heater, pouring into inner-layer carbon steel, performing metal liquid casting and manufacturing an interface metallurgical bonding cladding type double-metal composite blank; hot-rolling the cast double-metal blank to form cladding double-metal round steel and threaded steel. The metallurgical bonding interface of the stainless steel layer and the carbon steel core is formed by casting, and the advantages of high bonding strength, excellent processing property, dense structure, high quality, few procedures, low cost, high efficiency and the like are achieved. The integral stainless steel reinforcing steel bar is replaced by the double-metal reinforcing steel bar, so on the premise of guaranteeing the corrosion-resistant characteristic of the reinforcing steel bar, the stainless steel material is saved, the engineering cost is reduced, the strength of the reinforcing steel bar is effectively improved, waste of resource and energy and environmental pollution are reduced, and a wide application prospect is achieved.