A double step shot glue system of injection molding machine was presented. Two cylinder balance structure of the injecting system was discussed, and its working principle was described. The link dynamics equation and transfer function were presented. Through comparative analysis, the advantages of the two cylinder balance structure included improving injection pressure effectively, keeping operation stability well. At the same time, extra large injection and high injection accuracy were fit for a wider range product. So the double step shot glue system is more versatile, useful and valuable. It makes the injection molding machine more streamlined, optimal, affordable, efficient and highquality.