In order to study aerodynamic characteristics of a structure undergoing sudden change flow, a test for simulation of sudden change flow with an active control wind tunnel was introduced. Firstly, a gust velocity profile of downburst was simulated with the wind tunnel. Subsequently, a time history of wind speed change was simulated using step flow method. Finally, high-rise structure models were ... [Show full abstract] placed in the sudden change flow, and the variation characteristics of wind pressure on the structure surface and aerodynamic parameters in the flow were observed and studied. The results showed that the identities between the gust velocity profile simulated with the wind tunnel and the theory formula were more than 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 structure surface meanwhile.