In this work, visualized experiments were conducted to reveal the fundamental mechanisms of nucleation and growth using high-pressure foam injection molding (HP-FIM) with and without mold opening (MO) using a real-time in-situ visualization system. Results from both molding methods showed significant differences in nucleation and growth behavior and final foam morphology when different packing pressures were applied. A simulation strategy is proposed to predict the bubble growth profile in both HP-FIM and HP-FIM + MO. The simulation is composed of three main components 1. The Cell model, 2. Material and transport properties which are functions of temperature, pressure, and blowing agent concentration, 3. The Simha-Somcynsky equation of state. Simulation was conducted on both molding methods. The predicted growth profiles for both trials were in quantitative agreement with experimental findings. Sensitivity analysis was also conducted, the resulted growth profiles under different conditions were in qualitative agreement with the literature.