The effect of scrap iron drop in the die trimming on site production in the automatic production line was discussed, and the reasons were also summarized. The reasons of scrap iron drop in the die trimming which usually occurs in the die technological design were then analyzed in two aspects. Furthermore, the precautions were represented accordingly. On one hand, a discharge device was added based on the existing die-trimming structure. One the other hand, the trimming method was modified. By modifying and optimizing the trimming method, the scrap iron drop in the die trimming was significantly reduced, the product quality and accuracy were ensured, and the productivity of the automatic production line was improved.