Supersonic blowdown wind tunnels provide controlled test envi ronments for aerodynamic research on scaled models. During the experiments, the stagnation pressure in the test section is required to remain constant. Due to nonlinearity and distributed character istics of the controlled system, a robust controller with effective flow control algorithms is required for this type o f wind tunnels. In this paper, an extended Kalman filter (EKF) based flow control strategy is proposed and implemented. The control strategy is designed based on state estimation o f the blowdown process under the EKF structure. One o f the distinctive advantages of the pro posed approach is its adaptability to a wide range of operating conditions for blowdown wind tunnels. Furthermore, it provides a systematic approach to tune the control parameters to ensure the stability o f the controlled air flow. Experiments with different ini tial conditions and control targets have been conducted to test the applicability and performance o f the designed controller. The results demonstrate that the controller and its strategies can effec tively control the stagnation pressure in the test section and main tain the target pressure during the stable stage of the blowdown process.