In this article, an elementary method, which based on interfacial polymerization of aniline and intermacromolecular force between polyaniline and polyethersulfone, is proposed to construct a whole-polymer membrane electrode (PANI-FME) for flexible supercapacitors. The concentrations of H2SO4 and ammonium persulphate in coagulation bath have great influence on the basic membrane structure, electrical conductivity, and electrochemical performance. The area specific capacity achieves a maximum value of 1465.2 mC cm−2 at the current density of 0.5 mA cm−2. Furthermore, a device of asymmetric supercapacitors by employing the prepared electrode membrane as the positive electrode and the active carbon flexible membrane as negative electrode exhibits a high specific capacity of 585 mC cm−2 at 0.5 mA cm−2, an energy density of 813 mWh m−2, and a power density of 24.95 W m−2.