Abstract: The side heater in FOCKE401 overwrapper was improved to avoid the defective packets, such as loose and wrinkle film wrap, air bubble in side seal, etc. By analyzing the film characteristic and slot width, it was found that wide heating surface, static, inertia and centrifugal force were prone to cause film wrinkle. Therefore, the widths of pre-sealing heater and arc plate slot were set at 0.6 mm and 0.8 mm, respectively; and an electrostatic eliminator was added in front of the last driving roller. After improving, the appearance score of finished packets increased from 89 to 97, the operation efficiency of equipment raised from 78% to 85%, and the running speed of machine increased from 350 packet/min to 370 packet/min.