Based on the GOES-9 satellite IR images during inundation from 21 June to 22 July 2003, the mesoscale convective systems are investigated over the Huaihe River region. The results revealed: (1) There are total 10 and 24 , the frequency is much larger than the average of an ordinary year. (2) The large number of MCS originated and maturated in Huaihe River region is a main cause of this inundation. (3) The formation time of some of MCSs is different from general MCS. (4) The synoptic environment conditions of the MCS are various.