Abstract: In order to realize large-scale unsteady simulation of the downburst outflow in the atmospheric boundary layer wind tunnel, a set of large-scale test facility for the transient downburst outflow was designed and manufactured based on the plane wall jet method. The vertical profile of the horizontal mean wind velocity of the downburst was obtained by adding the wall jet device, and then the unsteady wind field was formed by using a fast-opening valve. The wind velocity record from the Andrews Air Force Base downburst is employed for verification of the experimental procedure. The results show that the simulation device of downburst based on wall jet can effectively simulate the wind field of downburst outflow. Under steady-state conditions, the test device can form a relatively uniform two-dimensional wall jet flow field, and in the fully developed area, the results are consistent with the vertical mean wind profile of the typical downburst flow. The time-varying mean wind velocity time history which is very close to the actual downburst record can be obtained by using the unsteady wall jet device.