PEMFC is increasingly used as power sources for eco-friendly transportation systems. In this study, the effects of air inlet temperature and relative humidity on PEMFC stack power were analyzed using AMESim. The stack power increased with relative humidity and then decreased under high-humidity conditions. The maximum stack power of approximately 32,340 W was obtained at 80°C and 60% RH. These results can provide fundamental data for determining operating conditions and developing thermal management strategies for fuel cell systems in small special-purpose vehicles.