It is a big challenge to well control the porous structure of carbon materials for supercapacitor application. Herein, a simple in-situ self-templating strategy is developed to prepare three-dimensional (3D) hierarchical porous carbons with good combination of micro and meso-porous architecture derived from a new oxygen-bridged porous organic polymer (OPOP). The OPOP is produced by the condensation polymerization of cyanuric chloride and hydroquinone in NaOH ethanol solution and NaCl is in-situ formed as by-product that will serve as template to construct an interconnected 3D hierarchical porous architecture upon carbonization. The large interface pore architecture, and rich doping of N and O heteroatoms effectively promote the electrolyte accessibility and electronic conductivity, and provide abundant active sites for energy storage. Consequently, the supercapacitors based on the optimized OPOP-800 sample display an energy density of 8.44 and 27.28 Wh·kg⁻¹ in 6.0 M KOH and 1.0 M Na₂SO₄ electrolytes, respectively. The capacitance retention is more than 94% after 10,000 cycles. Furthermore, density functional theory (DFT) calculations have been employed to unveil the charge storage mechanism in the OPOP-800. The results presented in this job are inspiring in finely tuning the porous structure to optimize the supercapacitive performance of carbon materials.