Based on the Doppler radar data, surface observation and rawinsonde data collected from April to September during 2000-2017, 35 squall line cases in the YangtzeHuaihe Area are identified. These squall lines occur most frequently in the plain to the north of the Yangtse River. The squall lines peak in July and a large proportion of them generate in early afternoon, mature in late afternoon, and dissipate in evening. The squall lines have a dominant southeast motion at the speed of 8-16 m·s-1. They are characterized by the maximum length of 200-250 km, the maximum intensity of 60-65 dBz, and the duration of 3-4 h. The squall lines commonly form in a brokenareal pattern, display a trailingstratiform pattern, and dissipate in a reversed brokenline pattern. The ambient flows of the squall lines are classified into five synoptic patterns, which are preshort trough, prelong trough, cold vortex, around subtropicalhigh and posttrough patterns. About 62.9% of the squall lines form in the dominant pretrough pattern. Prelong trough squall line causes the largest surface cooling. The radar echo cores of prelong trough and cold vortex squall lines are higher and the weather is more severe. Besides precipitation and thunderstorms, hail or tornado can also occur. Favorable conditions for the different patterns have been analyzed in the terms of instability, vertical wind shear and so on.