A novel control design method that is capable of linearly electrostatic driving a tunable capacitor is proposed in this paper. By extending the derivation of electrostatic theory and elastic theory in constructing the tunable capacitor, the nonlinear relationship between applied voltages and displacement (air gap) between two parallel plates of the capacitor is obtained. To suppress the nonlinearity so that the gap between the capacitor can vary linearly with the applied voltage, a control design method based on the variation of the multi-rectangular electrodes and applied voltages is proposed. By varying the number of rectangular electrodes that are evenly divided according to the size of the upper plate of the capacitor, the working space of the tunable capacitor with nonlinear characteristics is obtained. With this working space, linear control design method based on fixed or linearly varied applied voltages can be used to determine the number of the multi-rectangular electrodes such that stepping effect of the tunable capacitor can be achieved. Examples are used to demonstrate the feasibility of the present control design. Simulation results indicated that the linear control design method matched closely with the analytical analysis.