Due to the differences of filling density in filling machines, there might be some errors in roll reduction among rolls of the same cut and length. To avoid the rejects, the automatic complement system has been designed to connect with the roll reducing machine, which will automatically figure out the actual length. Meanwhile the PLC finds out the discrepancy between the actual length and the lengths required, so as to convert the length scope of sizing reduction. When the roll is taken into the automatic complement machine, the head and the end of the roll are not reduced in size, while the middle part will be sizing reduced in order to make up for the length required. The sizing reduction is about 0.10 mm. This method will be more effective than the stretching operation and produce less rejects. Besides, the complement machine and the roll reducing machine are connected to work together, which will be procedure-friendly and cost less.