A 56-day aging test of polyvinyl chloride (PVC) cable material under hot and humid conditions was conducted, followed by tests on flame retardancy after varying degrees of wet heat aging, including vertical burning behavior, oxygen index, and afterflame time. Using molecular dynamics simulation theory, the molecular mechanism behind the changes in flame-retardant properties after wet heat aging was investigated based on experimental observations. The results indicate that, as wet heat aging progresses, the flame brightness decreases, the oxygen index increases, and afterflame and afterglow times significantly decrease in vertical combustion tests. These findings suggest that the flame-retardant properties of PVC improve as moist heat aging deepens. After aging, the combustibles within PVC samples diffuse more easily, and the precipitation of CaCO₃ on the PVC surface enhances surface density, intermolecular forces, and thermal stability, which are key factors in the improved flame retardant performance.