The invention provides a preparation method for double-phase forming steel, which belongs to the technical field of high-intensity steel for automobiles. The steel comprises the following ingredients by mass percent: 0.1 to 0.5 percent of C, 0.3 to 2.5 percent of Si, 1.0 to 3.0 percent of Mn, 1.0 to 3.0 percent of Al, at most 0.02 percent of P, at most 0.01 percent of S, at most 0.01 percent of Nand the balance iron and unavoidable impurities. A production process comprises the following steps of: smelting, hot rolling and hot forming process simulation after the hot rolling. The controlled process parameters are as follows: hot rolling plate blanks are heated to 1200 to 1250 DEG C, the heat insulation is carried out for 0.5 to 1 hour, the final rolling temperature is 800 to 900 DEG C, and the coiling temperature is 600 to 700 DEG C. The hot forming process comprises the following steps of: carrying out heat insulation for 5min at the heating temperature being 750 to 850 DEG C and cooling the materials to the room temperature at the speed greater than 40 DEG C/s. The preparation method adopts the Al micro alloying treatment. Compared with the traditional thermal forming manganeseboron steel, the double-phase forming steel has the advantages that: 1, the hot forming heating temperature is low, and the surface oxidation is reduced; and 2, tissues after the hot forming are ferrite and martensite double-phase tissues.