In an aero gas-turbine engine, the demand of air-oil heat exchanger increases due to decreasing an oil temperature on the surface of gearboxes and electronic devices. Among the various types of heat exchanger, surface air-oil heat exchanger (SAOHE) with plate-fin is used for enhancing the performance of heat transfer. In the present study, the plate-fin type of SAOHE was adopted by using the two-dimensional porous approximation in the fin region for evaluation of the aero-thermal performance. Governing equations of mass, momentum and energy equations based on the compressible turbulent flow were solved using the ideal-gas assumption for the air. In order to consider the effect of mounting location of SAOHE, the six different locations were employed on the engine core and casing side. Using the porous media model, the pressure drop and heat transfer performance of the heat exchanger were predicted, and the results were compared with three-dimensional computational fluid dynamics results and experiment data for validation.