Based on a 1.5 L naturally aspirated engine using EGR technology, the optimized matching and analysis of EGR system were carried out, focusing on the simulation analysis and experimental verification of EGR gas extraction position, EGR uniformity of each cylinder, and EGR using conditions involved in the application of EGR system. Combined with the simulation and test results, EGR was selected to take gas before catalyst, and the EGR return air position was optimized, so that the deviation of EGR rate of each cylinder was controlled within ±0.5%. The temperature of using EGR was suggested to be not lower than 5 ℃ at the altitude of 0 km, and could drop while the altitude increased and the temperature of engine coolant should be between 55 ℃ and 110 ℃. The altitude proposal of using EGR was that the EGR rate should be corrected at the altitude of lower than 3 km by comprehensively considering the economy, the power performance and the achievability of ECU control.