The invention provides a method for shortening an injection molding period. The method comprises the step one of mold assembly; the step two of ejection pressure maintaining; the step three of cooling and feeding; the step four of mold pre-opening, wherein mold locking pressure is adjusted to be 70%-90% of preset mold locking pressure, then a movable mold and a fixed mold are opened to the preset distance so as to relieve high pressure in the mold, the preset distance is smaller than the mold opening distance, and the preset distance is increased along with increase of the mold locking pressure; the step five of mold opening, wherein the mold is opened to the mold opening distance needed for taking out finished products, the finished products are ejected, and one forming period is finished; and the step six of reciprocating from step one to step five. The method has the beneficial effects that in the product cooling process, the mold locking pressure is adjusted to be 70%-90% of the preset mold locking pressure, the movable mold and the fixed mold are opened to the preset distance, high pressure relief time needing to be consumed by the products after cooling is shortened, high pressure relief time of the cooled products in the cavity is shortened, and the purpose of shortening the period of product production is achieved.