The open-cathode proton exchange membrane fuel cell stack is an air-cooled stack, and has the characteristics of small footprint and high power density because of its unique configuration, combining oxidizer and coolant via axial fan. Depending on the demands of the application, proton exchange membrane fuel cells inevitably operate in harsh environments, such as high pressure, low or high temperature, etc. In this study, the performance of a 10-cell open-cathode PEMFC stack under thermal radiation was evaluated. The variations in cathode air temperature and relative humidity, stack temperature, output power and single-cell voltage under three different radiant heat fluxes were obtained by changing the load current and cathode air flow rate. The experimental results show that, even if the thermal radiation is beneficial to improve the stack temperature, the stack performance is not improved in all tested cases. Conversely, the degradation of stack power and failure of the stack continuous operation can be observed, especially for higher radiant heat flux, higher load current and lower air velocity. For the highest radiant heat flux in current study, the temperature of the first single cell closest to the radiant heat source exceeds the maximum allowable operating temperature of 65 degrees C due to the insufficient capacity of air cooling and the heating effect of radiant heat source. The significant drop in the first single-cell voltage results in the rapid degradation of the overall performance of the stack, and finally the stack fails to run continuously.