Abstract: A squall line weather process on 2 May 1998 was analysed over the eastern Anhui-Jiangsu provinces. The analysed result shows that there was a deep convergence layer on the low level, and severe divergence layer on the upper; the axis of low stream let stream on the low level was almost coincident with the axis of high value of the θse field. So that the space of the squall line not only had abundant energy storage, but also was favourable to the release of disturbance kinetic energy. In the crossing site of the gravity wave along the low jet stream and that of forward sector of backflow, the impulsive force might be very strong, and a squall line just appeared there.