Abstract Today, in injection molding field, the mold temperature control is a key point in the processing. With a high mold surface temperature, the quality of the part will be better, although the cooling time will increase and the cycle time will rise as well. The decreasing of the mold surface temperature will reduce the cooling time, but there is no benefit for the surface quality of part. Therefore, a critical requirement for current studies is to increase the mold surface temperature and still maintain a cycle time which is not too long. Induction heating is one of the most popular of external heating methods. However, in the heating period, there still have troubles when induction heating is applied for the pre-heating of injection molding plates. Therefore, for improving the heating process by induction heating, this research discussed about the application of inductor assistance device (IAD) for induction heating process to improve the heating process for injection mold plates. In this study, by simulation and experiment, the effect of the IAD on the process of induction heating will be discussed. Next, the effect of inductor assistance device position on the heating process will be clarified. Finally, an application of IAD on the corner mold plate with a rectangular inductor will be done for checking the useful of IAD in induction heating. As a result, the heating effect of cavity wall can be reduced efficiently with a proper design of IAD. With the molding area, the IAD can also reduce the different temperature from 62oC to 23.6oC, as well as improve the molding area from 189.3 mm to 264.1 mm with the length and 28.0 mm to 39.4 mm with the width of the rectangular inductor. It depends on the molding area that we need to heat; the rectangular inductor with the proper IAD can be used for heating a rectangular molding area, or two small rectangular molding areas. In this research, all the simulation has a good agreement with the experiment.