The role of eddies in the seasonal changes of general circula-tion over the Northern Hemisphere is studied by means of Eliassen-Palm theory. It is found that eddy transfer of baroclinic energyfrom the lower troposphere over the mid-latitudes to the subtropical tropopause region is closely related to the seasonal varia-tions of position and instensity of the subtropical jet stream. The response of zonal mean flow to the force of eddies is evident inearly summer with a sudden shift of the jet stream but only barely discernible during the shift in late autumn. Calculations showthat the enforced action of the eddies is favorable in maintaining acceleration of the westerlies to the north of the jet stream. The contributions of eddy transfer, diabatic heating and vertical diffusion are evaluated respectively by using a two-dimensional diagnostic model. Changes in the heating field are found to playan important part in the seasonal variations of the general circulation pattern whether in early summer or late autumn where a seffects of vertical diffusion of turbulent motions is more pronounced in late autumn.