Abstract: In reducing the prominent combustion noise during diesel engine idle conditions, exclusive use of exhaust gas recirculation （EGR） and pre-injection technologies has been proven effective. However, the synergistic effects of their joint application remain inadequately explored. A combined strategy of EGR and pre-injection cooperative control was proposed. By analyzing the independent influence mechanisms of the two on the combustion process （pressure rise rate, heat release rate, in-cylinder pressure spectrum）, an experimental scheme was designed to verify their cooperative noise reduction effect. Theoretical analysis and experimental results indicate that pre-injection reduces the premixed combustion amount of the main spray by creating a pilot flame core, which has complementary and synergistic potential with EGR in reducing the pressure rise rate during the initial combustion stage. The combination of the two exerts a synergistic enhancement effect. Under idle condition of a certain diesel engine, the combustion noise was reduced from 80.9 dB（A） with pre-injection alone to 79.0 dB（A）, while maintaining good combustion stability.