Abstract: Using simple dynamic model based on the theory of CISK, this paper discusses the influence of basic flow with horizontal change of vertical shear and with non-thermal wind on the formation and development of tropical cyclones. Theoretical study shows that when cyclonic vorticity increases with height in lower troposphere and anticyclonic vorticity increases with height in upper troposphere, and when there exists non-thermal wind in the opposite direction of the thermal wind, tropical cyclones are likely to form and develop easily.