The invention relates to a preparation method of a corrosion-resistant composite steel plate. The preparation method comprises the steps that (1) two low-carbon steel and a piece of stainless steel are stacked, the stainless steel is made to be located between the two low-carbon steel to form a composite billet, and gaps around the composite billet are welded through seals; (2) the composite billet is sent to a heating furnace for heating; (3) rolling and cooling are conducted; and (4) straightening is conducted, specifically, a rolled composite plate is subjected to straightening treatment, after straightening, the composite plate is placed on a cooling table for cooling, and when the surface temperature is reduced to be 300 DEG C or below, the composite plate can be taken down for cutting, a plasma or flame cutting mode is adopted to cut the composite plate, and after the head, the tail and the two edges are cut and surface grinding, performance detecting, packaging treatment are conducted, the corrosion-resistant composite steel plate with the required specification is finally obtained. The composite steel plate prepared through the preparation method of the corrosion-resistantcomposite steel plate is high in yield strength, high in tensile strength and good in pitting corrosion resistance.