The relationship between thermal wind helicity and severe convective weather is analyzed by calculating the helicity from 1000 hPa to 100 hPa, 1 to 31 July 2006 at Datong of Shanxi Province. The result shows that there was a high value center of thermal wind helicity before the severe weather occurred, and the higher the value was, the severer the weather was. This center appeared 6 hours before severe weather occurred. The thermal wind helicity can be used as an indicator in forecasting severe weather.