<p>This study visualized and recorded the foaming process of a polypropylene/azodicarbonamide (PP/AC) system using in-situ observation equipment. The obtained data were fitted and analyzed using nucleation and growth models. By combining real-time pressure measurements from sensors integrated into the visualization mold, the influence of the cavity pressure environment on cell nucleation and growth was systematically investigated. The results demonstrate that adjusting the cavity volume and shot size can effectively modulate the internal cavity pressure. Building a higher cavity pressure is beneficial for improving the thermodynamic stability of gas/polymer systems. Meanwhile, the pressure drop generated during the core-back process induces extensive cell nucleation within a short period. The final foaming quality is simultaneously affected by the cavity pressure and pressure drop rate. Additional experiments with increased foaming agent content confirmed that foam quality continues to improve with higher initial cavity pressure.</p>