Abstract: In order to meet the installation requirements of different aerodynamic models, the wind tunnel is designed as a structure with removable test segment, so that the original small closed-mouth wind tunnel can become an open wind tunnel by removing the test section. In order to improve the flow field quality of the open wind tunnel, a set of rectifier devices are designed including a collector and a small shrink section. Using CFD method, the flow field numerical values are simulated for different types of wind tunnels, and the turbulence model uses the SST k-ω turbulence model. At the same time, the Cobra probe is used to test the actual types of wind tunnel flow field, mainly to study the change trend of the speed uniformity and turbulence intensity, and to evaluate and compare the flow field quality of wind tunnels. Experimental and numerical simulation results show that the simulated speed and turbulence intensity profile are consistent with the measured. At a specific average wind speed of the wind tunnel test segment, the closed-mouth wind tunnel has the characteristics of low turbulence strength and high flow uniformity, and its central region turbulence intensity is below 0.3%. In addition, it is proved that the design of this rectifier can improve the flow field quality of the open wind tunnel. When the wind speed of the wind tunnel test section is about 50% of the maximum speed, the central area turbulence is below 0.5%, and the thickness of the boundary layer is reduced to 50 mm. These conclusions will lay the foundation for the design and improvement of small wind tunnel installations.