The invention discloses a blocking device for a smelting furnace for casting aluminum products, belonging to the technical field of aluminum product production. The blocking device comprises a long rod and a choke plug, wherein the chock plug comprises a tip and a choke body; the surface of the chock body is composed of a plurality of circles of round threads of which the diameters are gradually reduced towards the tip; each of the long rod and the chock body is of a hollow structure and is internally provided with a cooling water circulating pipeline; the diameter ratio of every two adjacent round threads is 1:1.2 to 1:1.5; the blocking device also comprises a supporting rod located at the end of the long rod, and the length of the supporting rod is larger than the width of a sliding chute. According to the blocking device, the round threads are arranged outside the choke body, and the cooling water circulating pipeline is arranged in the choke body, so that the contact area between a melted liquid and the choke body is increased, the melted liquid which is in contact with the choke body is rapidly cooled, and the blocking device is capable of rapidly blocking a furnace eye, good in blocking effect, simple in operation and capable of saving time and labor.