The invention discloses a vacuumizing mechanism for a mould. The vacuumizing mechanism comprises a base, an air exhaustion insert, an air exhaustion valve needle, an air outlet insert and an air exhaustion valve needle driving device, wherein the air exhaustion insert, the air exhaustion valve needle and the air outlet insert are all arranged in the base; an air outlet channel is arranged in the air outlet insert; a hollow part is arranged inside the air exhaustion insert; one end of the hollow part of the air exhaustion insert is communicated with the air outlet channel in the air outlet insert; the air exhaustion valve needle penetrates through the air outlet channel of the air outlet insert and is arranged in the hollow part of the air exhaustion insert; an outer protruding ring of which a radial direction is toward the outside is arranged at the outer circumference of the air exhaustion valve needle; an inner protruding ring of which a radial direction is toward the inside is arranged on the inner wall of the air exhaustion insert; and the inner protruding ring is opposite to the outer protruding ring. The vacuumizing mechanism for the mould at least has the advantages that the problem of air trapping in a mould chamber can be solved, so that the maintenance period of the mould is in normal time, the maintenance cost is greatly reduced, the quality of the injection molding product is more stable, and the product almost has no defective products.