Abstract: The research focuses on specific dimension of an injectionmolded plastic cover for miniature circuit breakers. Effects of five major parameters on the dimension were analyzed based on an orthogonal method. A comparative investigation was performed on results obtained from the simulation by a Moldflow software and exact experiments. The results indicated that there is a significant overall increasing trend in the pack and hold parameters on the dimension. A mathematical model between the pack and hold pressures and the specific dimension was established by a singlefactor experiment, which provided a valuable reference for parameters adjustment during manufacturing and also supplied a necessary condition for automatic control of dimensions of injectionmolded parts.