It is an urgent demand to find an alternative model to replace the actual tube bundles area when using numerical simulation to study the Intermediate Heat Exchanger(IHX) of a Sodium-cooled Fast Reactor. An appropriate alternative model can be a substitute for the actual model of IHX in terms of heat transfer and fluid flow. Dual-mesh coupled heat transfer is used based on the porous media model in FLUENT to simulate the flow field of a simple shell-tube heat exchanger and get temperature, velocity and pressure field data of the primary and the secondary fluid simultaneously. The result meets well with that acquired from the calculation of an actual model which proves that the method in this paper is reliable and is able to reduce the modeling and meshing work.