Thunderstorm gale is one of the main threats to aviation flight. It is a far more difficult challenge to forecast the thunderstorm gale accurately. The WINDEX empirical equation proposed by McCann is applied to the Capital Airport. Using 54511 sounding data from 2006 to 2010, the WI values are calculated and compared to strong gusts triggered by thunderstorm at the Capital Airport. Finally the forecast process of strong gusts is established.