As for product structure and mold design. Optimize mold exhausting scheme, and exhausting channel should be particularly set at confluence of front materials of plastic melt in the cavity;optimize design of product structure and mold feed system (especially gate position and section dimension of gate) to avoid severely uneven wall thickness, wherein the gate should be set at the thick wall of plastic parts, and the section shape and dimension of gate should be suitable for the weight of plastic parts to avoid such occurrences as unbalanced flow, stagnation and track effect etc and to achieve rational flow of melt in the mold, thereby enabling the gas under extrusion of melt filling to be discharged smoothly through sound exhausting method during the extrusion, especially at the final confluence of melt.