the merit of the Gas-assisted injection molding—low injection pressure and locking force, thereby reducing cost for equipment, since gas-assisted injection adopts “ underfeeding injection”, wherein the fusant’s filling of the mold cavity is accomplished under the pushing force of gas in the fusant, the injection pressure required thereof is relatively lower and the locking force is also low ( which can be reduced by 25%–90%), thereby saving energy, prolonging the service life of molds and reducing manufacturing cost.