There were many tornadoes produced in the area between Tianchang of Anhui P rovince and Gaoyou of Jiangsu Province, and also [JP2]in Xinghua of Jiangsu Province between 0840-1000UTC[JP] on July 3,2007. It was one of the extreme weather events of 2007. High temporal resolution geostationary satellite of FY2C and 2D, Nanjing Doppler weather radar data and routine meteorological data were used in analyzing the evolution of the weather system. The main conclusion was as follows: The dynamic and thermal conditions for strong convection development were provided bythe combination of the short wave trough with cold dry air at high altitude, wa rm moist air advection at low altitude and the divergence field at the north of the ridge line of Tibet high pressure. After 0400UTC, two mesoscale convective c loud belts were developed in the coboundary area of Anhui, Henan, Hubei and Ji angsu provinces. One of them, corresponds to the shear line on Meiyu front and i s rather weak. The other was the fast developing squall line at the south of the first cloud belts and in front of the cold air mass. The weak convective cloud belt moved south slowly. The convective cells in it propagated toward east. The squall line moved from west northwest to east southeast. The strong convective c ells in it propagated from west southwest to east northeast. The tornadoes deve loped in the area where the convective cells in two mesoscale convective cloud b elts merged.