Abstract: Air-sea interaction as a possible origin of intraseasonal oscillation in the tropical atmosphere was studied by using a simple coupled air-sea interaction model. It is found that with no consideration of the atmospheric internal feedback processes such as the Wave-CISK modes there still exist an intraseasonal oscillation mode in the linear air-sea interaction system within the realistic range of parameters, and the mode can slowly propagate eastward or westward, or can be quasi-stationary, when coupling coefficient is changed. It is also found that the effect of wave reflection at the longitudinal boundaries does not play an important role in sustaining formation of the intraseasonal oscillation mode. The studies may provide a theoretical background for explaining the local features of atmospheric low-frequency oscillation observed over the tropical ocean.