Abstract: The barotropical instability for smaller scale disturbances superimposed on a large scale circle parallel vortex is investigated numerically.The growth rates of the orders of (10-4-10-5)s-1 are found at azimuthal wave numbers between 3.0 and 10.0.Then the most unstable mode for the disturbances is taken as the initial steamfunction field of a quasigeostrophic barotropical model and two numerical experiments whose integration times equal to sixty model hours are performed for more and less intense vortex, respectively.Results show that the initial small disturbances for the both all develop certainly and that vortex filaments exhibit in the edge of more intense vortex, which is somewhat similar to the observational phenomenon concering the outer structure of tropical cyclone.