Abstract: We analyzed a thunderstorm gale event triggered by squall line over the central Hebei province on September 21, 2017, using conventional sounding data, observational data at surface automatic weather stations, National Centers for Environmental Prediction (NCEP) 1°×1° reanalysis data, satellite cloud images and data from Doppler weather radar.The results show that the thunderstorm gale event occurs at the bottom of a high-level cold vortex and is directly triggered by a squall line, under favorable conditions of cold air behind a short-wave trough overlying low-level warm advection.Both water vapor content and thermodynamic conditions reach the mean level triggering strong thunderstorm gales in North China.Compared with conditions in summer, vertical temperature lapse rate and vertical wind shear in autumn are more suitable for developing a thunderstorm gale, although energy is not as sufficient as in summer.The intensity and shape of the squall line are similar to those of the radar-echo characteristics during summer thunderstorm gales.However, a higher threshold of low-level radial velocity is required for the early warning of squall line gale in autumn according to the area of low-level radial velocity exceeding the threshold.The squall line in autumn is accompanied by mesoscale systems at the surface, such as a convergence line of the wind field, and thunderstorm high pressure.The effect of density flow in a cold pool favors the formation of strong winds near the surface.