This work presents a facile strategy to develop a flexible polyaniline (PANI)-based supercapacitor (SC) with both high energy density and good capacitance retention. An electrode with a symmetrical sandwich-structured configuration (PANI/flexible porous support/PANI) is used as both working and counter electrodes for this supercapacitor. For a conventional electrode with PANI depositing on single side of the support (PANI/flexible support), the flexible support bends severely during the PANI electrodeposition process, which results in poor PANI deposition. On the contrary, for the symmetrical sandwich-structured electrode, due to the stress-compensation effect induced by this configuration, the support bending is significantly suppressed and thus PANI films with a good uniformity are realized. Moreover, the stress-compensation effect involved in the symmetrical sandwichstructured electrode can also effectively balance the stress caused by PANI expansion/shrinkage during its electrochemical charge/discharge operation, thus improving the mechanical stability. The symmetrical sandwich-structured electrode has larger PANI mass loading, better PANI morphologies and stronger mechanical stability than those of the conventional electrode. Consequently, the SC constructed by the symmetrical sandwich-structured electrode displays better electrochemical performance in terms of its larger specific areal capacitance (369.2 mF·cm-2 at a current density of 0.25 mA·cm-2), higher energy density (0.031 mWh·cm-2 at a power density of 1.21 mW·cm-2) and better cycling retention (93.2% of the retained capacity over 6000 cycles) than the SC constructed by the conventional electrode.