The rational design of micro-mesopores is a hugely challenging for porous metal-based nanomaterials. Here oxalic acid (H2C2O4) as control agent is proposed for the first time to prepare 3D optimal micro-mesoporous NiCo2O4/NiO/Co3O4 nanoflowers (NCNs). Theoretical and experimental analyses demonstrate NCNs-0.1 which are prepared by adding 0.1 g H2C2O4 possess optimal distribution of micro-mesopores. The optimal structure creates abundant active sites and fluent ionic channels. Beneficially, NCNs-0.1 electrodes deliver an enhanced specific capacitance of 1693F g(-1) at 1 A g(-1) and outstanding cyclic stability (88% capacitance retention after 6000 cycles). Further, the assembled NCNs-0.1//AC capacitor achieves excellent energy densities of 43.02 Wh kg(-1) at power densities of 820.29 W kg(-1). The current NCNs-0.1 confirms a practicable method to optimize the electrochemical performances of supercapacitors by utilizing H2C2O4 to construct 3D optimal micro-mesoporous nanoflower architectures.