This study focused on the improved designs of airflow management in container data centers having overhead air supply. The computational fluid dynamics (CFD) model is first validated with experimental results. Then, the impact of grille diameter, deflector angle, and air supply layout on the data center thermal performance is investigated. The results show that the larger grille diameter may reduce the volumetric flowrate through the upstream grille, causing insufficient air supply and strong hot-air recirculation at the first rack A1. By decreasing the grille diameter from 335 mm to 235 mm, the average rack cooling index (RCI) and supply heat index (SHI) can be improved from 25.4% and 0.292 to 65% and 0.258, respectively. However, implementing small diameter grilles is not an economic way for data center performance improvement as far as the energy consumption is concerned due to the high pumping power. Meanwhile, raising the deflector angle below 30 deg in grille S1 can provide moderate improvement on temperature of the A1 rack. A further rise in the deflector to 40 deg may impose severe deterioration with a pronounced hot-spot area. The data center performance can be improved by changing from center-cold-aisle arrangement to center-hot-aisle layout. The layout provides much higher return air temperature and the RCI and SHI can be improved by 32.7% and 34.5%, respectively.