Rapid heating cycle molding (RHCM) that actively controls the mold temperature during plastic injection molding (PIM) is an effective approach for weldline reduction. On the other hand, the higher the mold temperature is, the longer the cycle time is. In addition, the warpage should be taken into account for high dimensional accuracy. For high product quality and high productivity, it is important to minimize the weldline, the warpage and the cycle time simultaneously. In this paper, process parameters in RHCM are numerically optimized for minimizing the weldline, the warpage and the cycle time. Numerical simulation in PIM is generally so intensive that sequential approximate optimization that response surface is repeatedly constructed and optimized is used to identify the trade-off among the objectives. The mold temperature during heating time is maximized for the weldline reduction, whereas the warpage and the cycle time are minimized. Through the numerical result, the trade-off among the weldline, the warpage and the cycle time is clarified.