Abstract: In order to study the aerodynamic characteristics of the structure undergoing sudden change flow, this paper introduced the test on the simulation of sudden change flow by active control wind tunnel. Firstly, a gust velocity profile of Downburst was simulated by the wind tunnel. Subsequently, time history of wind speed changes was simulated by step flow method. Finally, high-rise structure models were prepared in the sudden change flow, and the variation characteristics of wind pressure on surface and aerodynamic parameters in the flow were observed and studied in this paper. The results showed that the identities between the gust velocity profile simulated by the wind tunnel and the theory formula were above ninety percent, and sudden change flow could generate a high unsteady lift on the whole high-rise structure and a big unsteady wind pressure on the surface of structure meanwhile.