Abstract: The performance of a proton exchange membrane fuel cell (PEMFC) stack was investigated at different ambient temperatures and humidities. The results show that the relative humidity and the temperature of the surrounding air significantly affect the performance of the PEMFC stack, and the maximum output power of the PEMFC stack increases sharply with the increase of relative humidity. While the relative humidity is less than 30%, or the ambient temperature is below 10℃, the performance of the PEMFC stack deteriorates.