Although the supercapacitor has the characteristics of fast charging?discharging speed and high power density, its charging?discharging system is vulnerable to the inherent nonlinear characteristic of converter and the impact of charging?discharging voltage disturbance. The main circuit of the charging?discharging system for supercapacitor is constructed with a bi?directional DC?DC converter, and the inductance and capacitance are designed under the conditions of current continuity and DC?bus voltage fluctuation in the allowed range. In order to enhance the robustness of the charging?discharging system, a control strategy with constant current is adopted and PI controller parameters are adjusted under the constant current mode. Simulation results show that the charging?discharging system for supercapacitor not only achieve the output current stably flowing through with small ripple, but also has strong robustness.