Abstract: In order to investigate the flow and heat transfer characteristics of nitrogen gas in porous medium copper foam， a numerical simulation analysis of copper foam filled in cold head heat exchanger of cryocooler is carried on by FLUENT software. The effects of porosity， pore density， and inlet flow velocity on flow and heat transfer are studied in detail. The simulation results show that the seepage performance is good and the fluid velocity drops slowly when the porosity is large and the pore density is small. As the porosity decreases， the fluid pressure loss increases and the heat transfer performance becomes better， but the trend gradually slows. Therefore， there exists an optimal porosity with a minimum ratio of pressure loss and temperature drop. As the pore density increases， the fluid pressure loss caused by non-sliding wall increases， and the heat transfer performance deteriorates.