The invention discloses a method for molding a dual-layer alloy-steel pipe. Carbon steel is adopted as an outer layer material of the dual-layer steel pipe; stainless steel is adopted as an inner later material. The method comprises the following molding steps: preparing a blank of the dual-layer steel pipe; boring the blank of the dual-layer steel pipe; uniformly heating the bored blank to 1170-1250 DEG C; carrying out hot piercing on the heated blank by virtue of a perforating machine and producing a hollow billet; carrying out hot rolling on the hollow billet by virtue of a rolling mill, and producing a pierced billet; and carrying out hot sizing on the pierced billet by virtue of a sizing mill and producing the dual-layer alloy-steel pipe. An interference fit composite technology is put into full play; the inner alloy and the outer alloy of the produced dual-layer alloy-steel pipe are firmly combined; the outer alloy is carbon steel and has high strength; the inner alloy is stainless steel and has good corrosion resistance; the precious metal is saved; the material cost is reduced; and meanwhile, a hot piercing procedure and a hot rolling procedure are adopted; the molding cost is reduced; the energy consumption is reduced; and the competitive power of enterprises is improved.