Tuning　the　microstructures　of　electrodes　plays　a　vital　role　in　enhancing　the　electrochemical　performance　of　supercapacitors.　In　this　work,　we　have　developed　a　simple　and　effective　way　to　tune　the　microstructures　of　graphene-based　electrode　by　assembling　different　sizes　of　graphene　sheets　under　vacuum　filtration　and　freeze　drying.　It　is　found　that　the　large-sized　reduced　graphene　oxide　(RGO)　sheets　(e.g.,　RGO-50)　are　assembled　in　large　and　nearly　parallel　structures　showing　poor　capacitive　performance　due　to　the　long　transfer　length　of　electrolyte　ions　in　the　layered　structure,　while　the　RGO　film　with　small-sized　RGO　sheets　(e.g.,　RGO-8000)　has　relatively　small　pores,　thus　showing　low　capacitance　on　account　of　low　electrical　conductivity.　The　RGO　film　with　moderate　RGO　sheets　shows　proper　porous　and　honeycomb-like　network　and　thus　has　the　largest　capacitance　(260.2 F g−1),　ascribed　to　the　balance　of　electrical　conductivity,　ion　diffusion　and　reaction　interface.　By　considering　their　microstructures,　a　theoretical　model　is　developed　which　can　describe　the　electrical　conductivity　of　RGO　films　assembled　by　different　sizes　of　RGO　sheets.　The　results　presented　herein　exploring　structure–capacitance　relation　of　graphene-based　electrode　may　provide　useful　insight　for　designing　high-performance　energy　storage　devices.　©　2020,　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature.