A mold-conveying device for an plastic blow-molding machines includes a machine base and an auxiliary mold base. The machine base is located under a main mold base for positioning the lower mold of a shaping mold thereon, provided with plural correcting rods fitted in correcting rod holes in the bottom base of the auxiliary mold base. Further, a power member is provided under the auxiliary mold base for raising or lowering the auxiliary mold base, and the auxiliary mold base is provided with a transmitting device having a transmitting member to match with a rack provided in the machine base for shifting the auxiliary mold base rightward and leftward in accordance with the blow-molding movements of the plastic blow-molding machines for carrying out mold conveying.