Green polymer was used flexible substrate for sustainable energy storage in the present work. Namely, degradable and flexible free-standing composite film electrodes were designed with porous polymer-based nanocomposite films (polylactic acid (PLA)/carbon nanotubes (PLA/CNTs)) as conductive and degradable substrates for supercapacitors, via facile in-situ chemical oxidation polymerization of aniline with rapid-mixing chemical oxidation polymerization technique. The effect of the synthetic condition on the electrical conductivity and electrochemical properties of the resultant nanocomposite films was investigated. The porous polylactic acid/carbon nanotubes/polyaniline (P-PCP) sample P-PCP-3-H-2, which was prepared with an aniline concentration of 0.1 mol L−1 in presence of the porous polylactic acid/carbon nanotubes (P-PLA/CNTs) composite film after heat-treating at 60 °C for 1 h, possessed the best comprehensive performance, excellent mechanical strength with tensile strength of 18.7 MPa, highest specific capacitance of 510.3 F g−1 in 1.0 mol L−1 sulfuric acid electrolyte, good cycling stability of 111.5% after 2000 cycles and favorable flexible stability of 93.4% after 180º-bending for 700 cycles.