Equipment used for gas-assisted injection molding generally comprises a common injection machine and a gas injection device. A gas injection device contains such three components as a gas injection system, an air nozzle and a special gas pressure control system. The gas usually used is nitrogen and the pressure and purity of gas pressure are determined by the molding materials and the shape of products. Wherein the pressure is generally at 5—32 MPa, with a maximum level of 40 MPa.