The feedback stability of axisymmetric MHD mode in tokamaks with unclosed shell has been studied analytically through solving directly the boundary problem of the perturbed magnetic surface in the vacuum region. For plasma torus with elliptical cross-section, a feedback system with conducting shell and active control coils has been suggested. The result shows that two unclosed shells arranged above and below the plasma have a very strong stabilizing effect. The re istive shell can suppress the modes with faster growth rate and the active coils can be used to stabilize the slower modes.