Abstract: Taking the East Asia severe cold wave in October 197s as an example, variations of barotropic energy conversions expressed in the spectral domain before and after the cold wave are investigated. Some abrupt changes, which are shown as follows, are found. Before this cold wave, kinetic energies of synoptic scale waves(n=4-8) were stronger than that of ultralong waves, but later, ultra-long waves became the strongest waves. Next, the wave of wave number 2 with the role of energy source for the others changed greatly. These abrupt changes were the characteristics of seasonal transition.