Using the NCEP/NCAR 1°×1° final analysis data, Doppler radar data and Guiyang sounding data, the thunderstorm occurred at Guiyang airport during September 9?10, 2010 was analyzed by circulation pattern, divergence field, vertical motion, moisture flux divergence, K-index and radar plane position indicator (PPI) images. It is indicated that the shear line in east of Sichuan moving to the southeast arises thunderstorm, which is caused by conversion of upper air steering flow under the weakened and east retired subtropical anticyclone in 500 hPa. The upper air divergence and low-level convergence provide a favorable condition to the vertical motion. The strong moisture flux provides an enough moisture condition to development and maintenance of convection. The sounding data and K-index reflect the instability air condition evoking the thunderstorm.