The invention relates to a preparation method for low-density steel with the strength and elongation product larger than 50 GPa.%, and belongs to the field of low-density steel. The preparation methodincludes the following steps of smelting, specifically, raw materials are put into a smelting furnace for smelting; casting, specifically, obtained molten steel is poured into a mold, and low-densitysteel ingots are obtained after cooling; hot rolling, specifically, the obtained low-density steel ingots are heated to 1150-1250 DEG C, heat preservation is carried out, and then at least two timesof hot rolling are carried out; solution treatment, specifically, the obtained low-density steel is subjected to heat preservation at the temperature of 1000-1100 DEG C, and quenching treatment is carried out; cold rolling, specifically, the obtained low-density steel is subjected to at least two times of cold rolling; and cooling after annealing treatment. In this way, the low-density steel is obtained. Through regulation of alloy elements and the machining process, the Fe-Mn-Al-C system low-density steel is obtained, and the morphology of the low-density steel is of a multi-phase structure including austenite, ferrite and kappa carbide, so that the low-density steel has high strength and good plasticity, and the strength and elongation product is larger than 50 GPa.%.