The swirl intensity retention is defined to evaluate the transient flow characteristics in cylinder. The flow field in reentrant combustion chambers for heavy-duty automotive DI diesel engines is simulated and analyzed by software FIRE provided by AVL Co. The swirl intensity retention is calculated by Matlab from the simulation data. Based on this, the optimized experiments for matching between the fuel injection system and combustion chambers with different reentrant diameter have been done. The results show that by selecting different size of reentrant combustion chamber, the flow field in combustion chamber can be organized effectively and the optimized intake swirl intensity can be found, and through optimization matching with injection system parameters and flow characteristics in combustion chamber, the engine performance and emissions can be improved effectively.