The invention discloses an extrusion forming device for a crank shaft and a crank throw for a large-size ship. The extrusion forming device comprises a lower molded cavity consisting of two lower sliding chutes and two lower side plates and an upper molded cavity consisting of two upper sliding chutes and two upper side plates, wherein the lower molded cavity is positioned above the upper molded cavity; a female die is arranged in the lower molded cavity; the inner side of each upper sliding chute is movably connected with a sliding block through an inclined rail; the sliding blocks can slide along the inclined rails relative to the upper sliding chutes; the contact surfaces of the lower surfaces, which are in contact with the lower sliding chutes, of the sliding blocks are slopes; the two upper side plates are fixedly connected with at least one cylinder; a plunger of each cylinder is fixedly connected with a male die; the male die is fixedly connected with the upper ends of pull rods; the lower ends of the pull rods are movably connected with the upper side plates. According to the extrusion forming device, the machining allowance can be greatly reduced, and the utilization rate of a material can be increased. The extrusion forming device can realize quick demolding and is high in continuous degree, so that the manufacturing period of a product is shortened, the working procedure is short, the efficiency is high, and the operation is simple. The invention also discloses a forming method for the crank shaft and the crank throw for the large-size ship.