The performance of the dredging gas of the parts box is relatively high. If the air trapped between the cavity and the parison cannot be completely or expelled as quickly as possible, the parison cannot be inflated quickly, and it cannot be in good contact with the cavity after inflation. Surface roughness, dents and other defects, surface text, pattern is not clear enough, affecting the appearance of performance and external shape, especially when the parison is extruded, there will be streaks or melt fracture. The poor gas flow will also prolong the cooling time of the parts box and reduce its mechanical properties, resulting in uneven wall thickness distribution. To this end, it is necessary to try to improve the performance of the unblocking gas injected into the parts box.