Abstract: Utilizing the daily data set from ECMWF for nine years of 1980一1988, the seasonal transition of angular momentum and EP-flux for the easterlies and westerlies in Northern and Southern Hemispheres are analyzed by qualtitative and quantitative means. The follow- ing results are found:(1) In the westerlies, there are remarkable seasonal rapid changes happened generally in April and in October. and this phenomenon in Northern Hemisphere is more obvious than that in Southern Hemisphere.(2) In the easterlies, there is a sudden change occuring in June over Northern Hemi-sphere, yet over Southern Hemisphere the seasonal transition of the easterlies is not obvious.On the basis of this evidence the difference of factors affecting the rapid changes of April and June is discussed.