Abstract: By taking account of the character of the occeanic general circulation in the eastern tropical pacific, a local zonally averaged model for the coupled climatic oscillation of air-sea system is constructed. The frequency analysis shows that the feedback mechanism of 'cloud-radiation-SST can stimulate a kind of oscillation of nearly three-year period,for the thermal inertia of the mixed layer of ocean is enlarged by the upwelling of cold water. Under the stochastic forcing of the 'weather noise', the system can produce the power spectrum of SST that is very close to the observation.