Abstract: With a simple tropical coupled ocean-atmosphere model, this paper presents an analysis to understand the relative role of the meridional and zonal wind stresses in the tropical unstable air-sea interaction. The roles of the zonal wind stress, the meridional wind stress and the both are considered respectively into the coupled system. It is demonstrated that the meridional component of the wind stress does not lead to any instability under the local thermal balance assumption, but it does lead to a weak instability under the sea surface temperature advection assumption. Unstable air-sea interaction is dominated by the zonal component of the wind stress, suggesting that ignoring the meridional wind stress is approximately legitimate in studying the tropical unstable air-sea interaction.