Abstract: The wide-angle diffuser (WAD) plays a vital role to restrain compressor wake distortion and to improve the flow quality before the heat exchanger in a closed-circuit continuous transonic wind tunnel. There is no reasonable path to design an optimal WAD with screens based on the design method of a conventional wind tunnel, such as the previous design experience and engineering correlations technology. The computational fluid dynamics (CFD) with proper boundary conditions was used to compare the performance of different configurations for capacity of separation control, the improvement of the outlet flow quality and decrease of the pressure loss. The position and opening to the sectional area ratio of screens has an important effect on the flow regimes inside and outlet of WAD based on the details of numerical results. The first screen should be placed at just before the separation point, and the ratio of opening to sectional area is between 0.6 and 0.66. It is recommended that the second screen is near to the outlet of WAD using the porosity of 0.56~0.66. Flow behaviors in WAD, such as uniformity, separation and turbulence level, were significantly improved by the certain combination of the parameters mentioned above. Further investigations on flow mechanism and pressure recovery efficiency were taken. It is concluded that the optimal design of WAD could be obtained in terms of numerical results.