A series of six axis symmetric equilibrium models for Jupiter's inner magnetosphere was constructed, upon which the motion of an Io-torus-generated, mass overloaded magnetic flux tube on a meridian plane of the inner Jovian magnetosphere was studied numerically via magnetohydrodynamics approach. The flux tube is represented as a one-dimensional filament, while the Jovian magnetosphere is represented as a two-dimensional stationary medium. With only cold plasma included in the model, such heavy filament is unstable. However, when both cold and hot plasma are included in the models, the heavy filament is stabilized by the huge thermal pressure gradient for the Voyager period. For the Galileo period, the situation is less definitive because there is no observation-based hot plasma pressure data available within 6.75 Jovian radii (RJ). Nevertheless, our simulations in two models suggested that even with both cold and hot plasma included in the models, the heavy filament is still unstable for this period. The filament moves outward toward the middle and/or outer magnetosphere due to the interchange instability. The mass elements in the unstable filament are propelled along its length by the centrifugal force toward the equatorial plane. This filament tends to be more stretched in the outward direction than its neighbors as time elapses. The outward moving speed of the filament within 7.1 RJ is comparable with the Galileo spacecraft's observation in the Io torus on 7 December 1995.