A numerical simulation is performed for the threedimensional laminar conjugated heat transfer in a concentric tube recuperator with longitudinal fins.The effect of the fin number and fin height on the friction and the mean Nusselt number Nu is simulated.The results gained show that the different fin heights and different fin numbers both have remarkable influence on the friction and the mean Nusselt number.The mean Nu changes with the change of fin number,within the scope of changing field,and reaches its max value.As the fin height increases,the Nusselt number at entrance,and the developed Nusselt number will increase aslo.