To improve the airflow and differential pressure in a cleanroom, recently a central return duct was used in a cleanroom. We Performed the numerical analysis on the airflow in the three type of cleanroom model, which are the general model, partition model and central return duct model. The airflow distribution, deflection angle, differential pressure distribution and air age were used to for analyzing the characteristics and performances of cleanroom. From the numerical results, we know that the central return duct not affect on the airflow, but is effective in improving differential pressure.