Abstract: Based on the tropical cyclone yearbooks, the NCEP/NCAR reanalysis data and the kinetic energy equation of rotational and divergent wind, study is carried out of the extra tropical transition and reintensifying of the landfalling Tropical Cyclone Haima(2004). The results show that, when moving toward the north pole, Haima couples with the jet before the upper westerly trough, which induces cold air to invade the circulation of Haima. Furthermore, the divergent wind kinetic energy equation is applied to diagnose the kinetic energy sources of the extra tropical transition of Haima. It is found that, one of them is from the released available potential energy by cold air’s invading the tropical cyclone circulation, and the other is the transformation from the total kinetic energy of uneven distribution in the circulation to the tropical cyclone kinetic energy via the divergent wind due to the interaction between Haima and the peripheral synoptic systems. Both are in the same magnitude, and able to enforce the low level wind of Haima increase up to 10 m/s within 6 h. The consumption of kinetic energy of the tropical cyclone is due to the land surface friction and atmosphere internal friction, and the divergence term of vertical kinetic energy flux causes the divergent wind kinetic energy to transport from low levels to upper levels.