Abstract: In this paper, the complete analytical solution of Kelvin wave is obtained by using the linearized equations on the equatorial β-plane and excluding external forcing. The vertical transport characteristics of energy and momentum due to this wave mode are further analysed. Provided that the phase propagates downward, the wave transports energy and westerly momentum upward. Then this theoretically shows that the vertical transport characteristics of energy and momentum due to Kelvin wave which have already been shown by other authors with observational data. It also indicates the role of Kelvin wave in the establishment and downward propagation of the westerly phase of the Quasi-Biannual Oscillation(QBO).