Abstract: With the consideration of characteristics of spectral average of the Rossby wave trains and the adoption of climate mean stream field, it can be proved that atmospheric action centers are low frequency oscillator with dipole structure, and that energy of low frequency oscillation originates from condensation heating and ocean heating It can deduced that the wave ray will move southward across the streamline in the mean wind field with south component or northward across the streamline in the mean wind with north component The switch of propagation takes place near the bottom of trough or the top of ridge A reasonable explanation can be given to the location of main teleconnection dipole and paths in the North Hemisphere at 250 hPa