Abstract: This paper applies the Hoskin's and Simmon's wave-flow interaction principle to analise the relationship between the zonally asymmetric barotropic instability in basic flows for 200 hPa and the 30 -50 day periodic oscillation from 1981 to 1982.It is pointed out that the jet stream exit is the strongest field of interaction between kinetic energy of 30-50 day oscillation, basic flows and low-frequency oscillation.The low-frequency oscillation acquires energy from basic flows and develops fully within a week.The Asian continent (40°N) and the middle part of the Atlantic (45°N) is a major energy source for 30-50 day summer oscillation, while the middle part of the Pacific (30°N) and Northern America coast (40°N) is a major energy source for 30-50 day winter oscillation.