The plate-fin heat exchanger is widely used in aerospace field because of its compact structure, small size and good economy. As the main part of the system, the accurate evaluation of heat transfer characteristics and flow characteristics of heat exchangers is directly related to the overall safety and stability of the system. In order to solve the problem of grid division caused by the complex structure of heat exchanger core and the shortage of calculation resources, a CFD simulation method for plate-fin heat exchanger core was proposed. The method can reduce the calculation difficulty and maintain sufficient accuracy. This study used the FloEFD software to simulate the simplified heat exchanger core. The accuracy of the simulation method is validated by comparing with the experimental results. The heat transfer characteristics and flow characteristics of heat exchangers under different flow rates were studied by the validated simulation model.