A mold structure contains: a first mold, an isolation washer, and a second mold. The first mold includes a ring-shaped closing rib arranged on a top surface thereof and a cavity defined in the closing rib. The isolation washer is formed in a ring shape and includes a melting point higher than a molding plate, wherein when the isolation washer retains with the fixing slot of the closing rib, and a top surface of the isolation washer is higher than that of the closing rib, the molding plate is held by the isolation washer. The second mold moves relative to the first mold to press a top surface of the molding plate, the second mold includes a close chamber defined on a bottom surface thereof and corresponding to the cavity and includes a gas supply pipe communicating with the close chamber and connecting with a high-pressure gas device.