Abstract: Based on the NCEP/NCAR reanalysis data in 2000-2006, the complete form vertical vorticity tendency equation is used to diagnose the thermodynamic structures of two sets of composite tropical cyclones (TCs), each composed of 5 tropical cyclones, whose intensity changed rapidly over the coastal waters of China. The study shows that maximum centers of apparent heat source Q 1 appeared in both the upper and lower troposphere near the center of rapidly strengthening TCs. The Q 1 maximum center in the lower troposphere became stronger during the rapid development of the TCs. But for rapidly decaying TCs, the maximumQ 1 cen ter formed in the middle troposphere near the center of the TCs, and it became increasingly weaker during the decaying process of the TCs. The peak heights of Q 1 of rapidly strengthening/decaying TCs were located in the upper/midtroposphere respectively. A maximum apparent moisture sink Q2 was found in the middle troposphere during the intensity changes of TCs. It became stronger and its peak height rose when the TCs rapidly intensified; whereas it became weaker and its peak height dropped when the TCs rapidly attenuated. This suggests that the vertical transfer of cumulus convection played an important role in the rapid intensification of TCs. The increase of the diabatic heating near the TC center with height in the midupper troposphere and the increase of the vertical inhomogeneous heating near the TC center in the lower troposphere were both favo rable to the TC sudden intensification. The reverse was true for the TC abrupt w eakening.