α-MnO₂ was synthesized via a fluid phase way, and prepared as an electrode. Then the symmetry supercapacitor was assembled. Constant current charge-discharge, alternate current (AC) impendence and cyclic voltammetry were carried out to investigate the electrochemical performance of the positive and negative electrodes respectively in charge-discharge processes. The results suggest that some electrochemical reactions occur in the positive electrode in 0.31～0.41 V and 0.43～0.50 V (all vs. Hg/HgO) and determine the voltage of the supercapacitor. However, the negative electrode is relatively inert, with no reactions occurring. Both reactive and contact resistances diminish with the increase of electrode potential. The negative electrode resistance dominated the supercapacitor, and for it, the rate of double-layer formation on the surface of the negative electrode was less than that of the positive electrode, while the degree of the influence of potential on the negative electrode was more than that on the positive one, and its charge-keeping ability was better than that of the positive one.