Abstract: In this paper, a squall process occurring behind the cold front in Chang Jiang—Huai He area is analysed with the help of the enhanced observational data. The analysis shows the genesis and development of squall are related to the mesoscale cold surge activities. The cold surge is characterized by the large amplitude gravity wave. The gravity wave is trapped by Dabie Shan Mountain in the process of propagation and the edge front is formed at the east side of Dabie Shan Mountain. The propagation of edge front shows the feature similar to Kelvin wave. The character of large amplitude gravity wave in the boundary layer is very obvious. This kind of large amplitude gravity wave trapped by the mountain may be a trigger mechanism of the squall line behind the cold front.