The invention discloses an extruding-rolling combined preparation method and device for composite boards. The method comprises the following steps of performing homogenization treatment on a metal blank; making a concave blank in an extrusion manner by a concave blank extrusion die; making a convex blank in an extrusion manner by a convex blank extrusion die; squeezing the convex blank into the concave blank with equal length and width to obtain a composite blank; rolling the composite blank. The device comprises the concave blank extrusion die and the convex blank extrusion die; each of the dies comprises an extrusion heat, an upper die block, a lower die block, a heating device, a temperature measuring device and a fastening device, wherein the upper die block and the lower die block arematched and fixed by the fastening device; one side of the space formed between the upper die block and the lower die block is matched with the extrusion head, and the other side is used as an extrusion working region; the heating device and the temperature measuring device are arranged on the upper die block or/and lower die block. The device has the advantages that die structure is simple; three-dimensional composition of the composite materials is achieved by the convex blank and the concave blank; binding force between base materials is increased; operation is convenient, cost is low, andindustrialization can be better achieved.