Abstract: MCSs (mesoscale convective systems) are significant weather systems causing heavy rain and other severe weather events during the warm season, which are very difficult to forecast in operation. Geostationary satellite infrared imagery with higher spatial and temporal resolution can provide much available information for MCS surveillance and forecasting. Since Maddox defined the MCCs (mesoscale convective complexes) based on enhanced satellite IR imagery, there are many detailed studies on the MCSs, but these studies revealed that Maddox's MCC definition is too strict. Then the MCS definition based on satellite imagery is always modified. In recent years, some studies classified MCS to MαCS (meso-α convective system) and MβCS (meso-β convective system). But because the definition of MCS based on satellite imagery is not uniform, it is very hard to compare various results of MCS census. First, the progress of MCS census research is reviewed, and the smallest horizontal scale of MβCS (meso-β convective system) is modified as that the diameter of cold cloud continuous area of TBB value≤-32 ℃ is more than 20 km. Secondly, based on the new definition of MβCS, the mesoscale convective systems are investigated over the Huaihe River Basin utilizing GOES-9 satellite IR imagery during June 21—July 22 2003, the results reveal that there are 10 MαCSs and 24 MβCSs. Comparing the definition of MβCS with that in the study of Ma et al, there are 7 MβCSs which can not satisfy the MβCS definition of Ma et al, and 6 of them lead to heavy rain over Huaihe River Basin. It shows that the new MβCS definition can better reveal the relationship between heavy rain and MCSs over the Huaihe River Basion. Finally, the other three typical MβCSs which produced heavy rainfall over Beijing are analyzed, Shalan Town of Heilongjiang Province, and Shanghai. The diameter of these three MβCSs is about 20—150 km, so they satisfy the new MβCS definition, but do not satisfy the MβCS definition of Ma et al. The results reveal that the new MβCS definition is very helpful to investigate and forecast the MCSs producing severe weather events in China.