It is a trough-shaped air outlet opened in the mold to discharge the gas that the original and the melt brought. When the molten material is injected into the cavity, the air originally stored in the cavity and the gas brought in by the melt must be discharged from the mold through the exhaust port at the end of the stream. Otherwise, the product will have air holes, poor connection, and the like. Dissatisfaction with mold filling, even the accumulation of air due to the compression generated high temperatures and burn the product. Under normal circumstances, the vent hole can be located either at the end of the melt flow in the cavity or on the parting surface of the mold. The latter is a shallow groove that is 0.03-0.2 mm deep and 1.5-6 mm wide at the side of the die. During the injection, the exhaust hole will not leak much molten material, because the molten material will cool down at this place and solidify the channel. The position of the exhaust port must not be facing the operator to prevent accidental ejection of molten material. In addition, the clearance between the ejector rod and the ejector hole, the clearance between the ejector plate and the ejector plate and the core, and the like can be used for exhaust.