Downburst is a strong downdraft generated below a cumulonimbus cloud, which hits the ground rapidly and causes significant low-level wind shear. It is a strong destructive regional weather phenomenon, which is the main reason for the transmission towers. In recent years, some scholars have researched the finer wind field characteristics and wind load of downburst by using the method of CFD. But the initial conditions are all assumed due to the small synoptic scale, the short lifecycle and the big measurement difficulty of downburst. So downburst wind load can not be taken into account in structural design. Based on the 3-D convective storm numerical model, by inputting temperature, humidity and wind fields detected in Wuhan radiosonde station at 8pm on July,27th,2007, simulation has been accomplished to understand the characteristics of the wind field in the place where the downburst incurred actually. The result provides model data and parameters for CFD simulation, which has directive significance to concern the high intensity downburst wind load in structure design.