Based on conventional observation data, automatic weather station data, NCEP(1°×1°) reanalysis data and Doppler radar data, the causes of formation, development and evolution process of four long life squall line on Jianghuai River basin have been researched. The main conclusions are: long life squall line needed strong unstable stratification, and the supplement of high cold air was one of the basic maintenance reasons of it. Coastal terrain in Jiangsu provided the long life squall line with a good water vapor condition. Intensive conditions, such as strong environmental vertical wind shear, upper jet and upper air divergence, all could maintain long life squall. The squall lines are charactarized by typical bow echo on the radar screen. The structure of mature bow echo was rigorous, the width was narrow and in front of bow echo, there was gust front. The vertical structure of the bow echo showed that on the inflow side of bow echo there was high reflectivity gradient, and the echo top was located above the strong reflectivity gradient zone. Squall line on Doppler radar radial velocity images was associated with the development of the wide low speed area and MARC at mid-level. The MARC and mesocyclones could be considered as early-warning of disastrous winds on the ground.