.In order to manufacture high quality intake port with bigger discharge coefficient and appropriate swirl ratio for diesel engine performance improvement, intake port tests and CFD simulation method were combined together to optimize its structure. The three-dimensional CAD model of intake port was built and was putted into AVL–FIRE platform to do CFD simulation with appropriate turbulence model and calculation method. The detailed air flow information was obtained by CFD simulation. After analyzing, two optimization programs were discussed. This research shows that CFD simulation is a powerful method to design diesel engine intake port; air flow condition is complex in the intake port; intake port structure optimization can increase the discharge coefficient and improve the air flow condition.