Abstract: With the assimilation data of the IOP period of South China Sea Monsoon Experiment, the comparison and study of mechanisms responsible for the generation, evolution laws and maintenance of kinetic energy in the South China Sea (Region C) and the Bay of Bengal (Region B) are made. The analysis shows that mean kinetic energy of the general flow in Region B grows explosively and the kinetic energy increases gradually with amplitude smaller than that in Region B when monsoon breaks out. The transport of kinetic energy in the cross-equatorial flow is important for the establishment of southwest monsoon in Region B. The kinetic energy flowing into the west boundary in Region C is also significant for the establishment of monsoon there. During the prevalence of monsoon, the evolution and variation of kinetic energy in southwest monsoon in Region B mainly depend on the contribution of divergence of horizontal flux while the kinetic-energy generating terms within Region C play the maximum role. For the 850 hPa layer, however, the baro clinic generation of kinetic energy plays a dominant role in Region B but more kinetic energy is reduced by the baro tropic process; energy is produced baro trocally in Region C. In the upper layers of the troposphere in both regions can be found the outflow of kinetic energy, but in the lower layers inflow of energy can be found in Region B and outflow of energy be found in Region C.