Abstract: In this paper, starting from the equations describing tropical cyclone, the spiral structure of the tropical cyclone is discussed and the flow pattern is described. It shows that the formation of spiral structure is due to the action of internal gravity-inertia waves,particularly internal gravity waves. The spiral form is connected with the phase velocity of waves. The "trailing" spiral structure in the Northern Hemisphere demands that the spiral lines move counter-clockwise and outward. The angle with which a spiral line intersects with a circle of radius r is ordinarily less than 45°,at the edge of tropical cyclone it is about 10°.The distance between the spiral "arms" is about 220 km for m=2, 110 km for m=4.The spiral waves of the tropical cyclone are dispersive. In the "trailing" spiral, cgr and cr are always positive, and cgrcr.It is found that, if the water vapor is enough and latent heat is more than enough,the tropical cyclone may mamtain.