The Partial Frame Process (PFP) is a kind of gas-assisted injection molding, fn which the void core is generated by imposing low pressure air into the molded part just after the resin is completely filled, after which the void grows as it compensates the volume shrinkage of resin. It resembles a secondary gas penetration step of gas-assisted injection molding, but has more advantages, such as its simplicity, design flexibility, ease of control, and cheap utilities. In this study, modeling of the void growth in PFP was carried out. By comparing the results with the experimental data, basic assumptions have been justified and the mechanism of the void growth could he explained in terms of the process parameters such as mold temperature, melt temperature, and the channel size. An experimental approach was also taken. As there are many factors affecting the process, the method of design of experiments was adopted, and the effects of the process parameters on the void growth length and the mechanism of the void growth were investigated. The results are expected to help in mold design and the determination of the operating conditions, as well as our understanding of this new process.