Abstract: Basing on the geostrophic approximation, the two-dimensional dynamical structure of the wind fields of Jupiter's Great Red Spot and White Oval BC is obtained.The results of calculation are in good agreement with the observations Thus, an explanation of the observed dispersion of the velocities along the horizontal streamline is given, The major physical mechanism of this dispersion is as follows The distance between two adjacent elliptical streamlines varies along the elliptical streamline, leading to the variance of the normal pressure gradient, Thus, the horizontal velocity V_T has to vary correspondingly so that the, Coriolis force can approximately balance the normal pressure gradient, Another less important factor, i,e, the change of the Coriolis force parameter f with the latitude,is also taken into account The distributions of the vorticities of GRS and White Oval BC are also calculated.