Traditional numerical simulation methods have shortcomings of large amount of calculation, longer calculating time, so they can not meet the development requirement of modern industry. A POD reduced-order model for flat tube fin heat exchanger is constructed by combining body-fitted coordinates with proper orthogonal decomposition. The flow and heat transfer process of flat tube fin heat exchanger is calculated under unique heat flux boundary conditions. And its calculation results are compared with calculation results of the finite volume method (FVM). Results show that the POD method is feasible for solving the flow and heat transfer problems in complex structures such as flat tube fin heat exchangers and that can accurately capture the temperature field and velocity field information for different parameters. The relative deviation increases with the number of variables between the POD and FVM. The relative average maximum error of reconstructed velocity fields and temperature fields are 1.90% and 0.308%, respectively. Both cases are three-variable conditions. The POD method can increase the calculating speed of the traditional FVM by 3093.4 times under the premise of ensuring the calculating accuracy. This study has certain theoretical reference for improving the numerical design efficiency of flat tube fin heat exchangers and expanding the engineering application field of POD method. © 2020, Editorial Board of CIESC Journal. All right reserved.