Based on the enahnced IR satellite imageries of the 30 springtime major rain events over Oklahoma, U. S., a survey of the mesoscale convective complexes (MCCs) was presented. The differences between the MCCs and the non-MCCs, the proportion of the MCCs in the mesoscale convective systems (MCSs), and the weather patterns, life cycle, inner structure and synoptic situations of the MCCS were all discussed.