1.Atmospheric and Oceanic Sciences,Department of Physics,Peking University，Beijing 100871,China; 2.Guizhou Air Traffic Control Bureau of CAAC,Guiyang 550012,China

By analysing a suddenly strong winds and rainfall weather event which happened on October 13th,2011,Guiyang airport,the results indicated that the process is a clear downburst event.Although no favorable synoptic scale weather systems,but the ground small scale convergence system triggered the development of convection process,strong divergence in the middle to high-level inhibited the development of convective cells' height .Low level convergence,upper level divergence generated effect of atmospheric compensation,and which strengthened the upward motion，convective cells developed rapidly.But lack of support of synoptic scale systems,convection was inhibited,the convective cells collapsed rapidly also.When the strong downdraft with precipitation strike to the ground,then resulted in the downburst.