Passive Containment Air-Cooling System (PAS) plays a critical role in mitigating temperature and pressure increases inside the containment during accident scenarios. The installation of radiation plates within the flow channel can effectively improve the PAS heat transfer performance. However, over time, factors such as aging, corrosion, and contamination can alter the surface emissivity of both the inner steel shell and the radiation plates. This alteration subsequently impacts the heat transfer efficiency of PAS. To investigate this impact, ANSYS Fluent 18.2 was utilized to perform numerical simulations on a simplified model of the ACP100 reactor. The results indicate that without radiation plates, a decrease in the surface emissivity of the inner steel shell leads to a gradual reduction in the PAS heat transfer performance. Specifically, when the emissivity drops from 1 to 0.5, the heat transfer power decreases by 8.6%. With the installation of a radiation plate, if the surface emissivity of both the inner steel shell and the radiation plate decreases simultaneously, the heat transfer performance of PAS is significantly impaired. In this case, a reduction in emissivity from 1 to 0.5 results in a 21.7% decrease in heat transfer power. Additionally, variations in the thickness of the radiation plate (ranging from 0 to 50 mm) have a minimal impact on the heat transfer performance, with changes in heat transfer power remaining below 2%. Therefore, it is evident that a decrease in the surface emissivity of the containment structure and radiation plates notably impairs the heat transfer performance of the PAS. As a result, in engineering applications, it is essential to implement regular maintenance measures to effectively mitigate the deterioration of surface emissivity.