Taking ACP100 small reactor as the research object, this paper conducts plate experiments and numerical simulation studies on the heat transfer phenomenon of passive containment air cooling system (PAS system), and studies the effects of different heating power and wall blackness on PAS system. The calculation results show that with the increase of heating power, the natural circulation flow rate increases significantly, which is conducive to heat exchange in the PAS system. The increase of wall blackness will increase the radiant heat transfer capacity and improve the radiant heat transfer of the PAS system. At the same time, the calculation results and experimental results are compared, and the results show that the numerical simulation is in good agreement with the experimental results, which verifies the accuracy of the model used in the numerical simulation process, and paves the way for further research on the heat carrying capacity of the small reactor PAS system.