The causes for the 6 May 2010 severe windstorm were analyzed in Chongqing by using conventional observations, NCEP analysis fields, radar and AWS (automatic weather station) data, etc. The results showed that the almost overlapping configuration structure of the cold front and the subtropical upper jet promoted the formation of secondary circulation with contributing to the development of strong upward motion near the windstorm area. It was significant that the atmospheric convective instability was strengthened by the underlying surface strong heating, the low temperature and humidity increasing and the drycold air in the middlehigh level in the day before the storm, which made for the formation of thunderstorm. The strong index gradient areas at the edge of the CAPE, K, SI highvalue area and the CIN smallvalue regions were significant indicators to forecast the strong wind and hail. The radar echo was characterized by threebody scattering, weak echo area, and hail echo. The midlevel radial convergence and the reflectivity core up and down repeatedly were also the important features of the surface gale and hail formation. The northeastsouthwest oriented mountain range blocked the cold air moving direction in eastern Sichuan Basin. The troughshaped terrain provided a larger space for the sustained development of multicell storm between the mountains. The south terrain of Mingyue Mountain played a role of uplifting and triggering. The narrow tube effect of terrain blocking enhanced the formation of downburst leading to the surface high wind, which was the important reason for the formation of 11 rank gales.