A mesoscale convective system(MCS)influenced Hunan Province during 11, 0900 -12, 1000 UTC June 1994 has been studied by the use of the scale separated kinetic energy. Results showed that (1 ) the kinetic energy generated by the ageostrophic flow in large scale motion field and by the interaction between the flow and pressure fields of the large-and meso-scale motions is the dominant source of energy; (2) the kinetic energy of the mesoscale motion and of the interaction between large-and meso-scale flow fields increases (decreases) with the MCS's development (fading);(3) the total kinetic energy of upper troposphere drastically reduced during the MCS's development phase.