Abstract: Under reasonable assumptions, the theoretical and experimental temperature distribution of polypropylene (PP) during the cooling stage in gas-assisted injection molding (GAIM) was studied via the numerical simulation coupled with experimental measurement. It showed that the cooling rate of PP was significantly increased after an injection of N2, and a small “crystallization platform” near the gas-melt interface was observed. The mathematic model was solved through the mathematical software package MATLAB and measurements of temperature profiles of PP and N2 showed good agreement with the numerical prediction during the liquid cooling process. During the solid cooling stage, the values of theoretical predictions of PP were larger than the experimental ones, while the values of theoretical predictions of N2 were lower than the experimental ones.