The pressure drop and heat transfer performance of an oil cooler were simulated on Ansys Fluent with the multi-scale method． In order to improve the simulation accuracy，the heat flux equation of the fins at arbitrary coordinates was established according to the simulation data of the micro-scale model in the oil cooler． The simula-tion conditions were 0. 001、0. 1、0. 2 and 0. 3 m/s on the hot side，and 0. 1、0. 2、0. 3 and 0. 4 m/s on the cold side，respectively． On that basis，the momentum source term equation and the heat flux equation were calcu-lated with the micro-scale model data． The pressure drop and heat transfer performance of the oil cooler were simu-lated under the condition that the mass flow rate on the hot side was 0. 04、0. 08、0. 12、0. 16 kg/s，respectively and the volume flow rate on the cold side was 5 × 10^-4 m³ /s． The research shows that the simulation data is in good agreement with the experimental data，and the relative error is within 10%． The accuracy of the multi-scale simulation method can meet the requirements of general engineering applications．