The　efficient　and　low-cost　method　to　produce　sustainable　energy　materials　for　supercapacitor　is　highly　sought　after.　Biomass　offers　great　opportunities　as　green　and　low-cost　raw　materials;　however,　the　extra　activation　and　multi-step　procedures　to　obtain　desirable　porosity　are　often　required.　Herein,　a　simple　and　economy　way　was　developed　to　synthesized　hierarchically　porous　nanocarbons　with　N-doping.　Microcrystalline　cellulose　was　chosen　as　the　carbon　precursor　and　thermally　treated　in　N2,　NH3,　and　CO2　atmospheres　in　tandem.　This　continuous　gas　treatment　enables　the　formation　of　functional　carbons　with　high　surface　area　and　abundant　porosity.　The　optimized　pyrolytic　carbon　HPNC-150　expresses　a　super　high　specific　surface　area　reaching　up　to　3278　m2　g-1　with　the　pore　volume　of　1.6291　cm3　g−1.　Electrochemical　tests　indicate　the　carbon　HPNC-150　delivers　a　specific　capacitance　of　221　F　g−1　at　a　current　density　of　1　A　g−1　and　remains　201　F　g−1　at　5　A　g−1,　and　thus　show　an　excellent　storage　capacity　for　supercapacitor　applications.　Besides,　it　was　found　that　the　competition　between　the　thermal　graphitization　and　CO2　activation　balances　the　hierarchical　porosity　and　electrical　conductivity,　which　is　a　good　reference　to　synthesize　the　porous　conductive　substrates　for　further　modifications.　©　2021　Elsevier　B.V.