Safely and highly selective acetylene (C₂H₂) capture is a great challenge, because of its highly explosive nature, as well as its nearly similar molecule size and boiling point toward the main impurity of carbon dioxide (CO₂). Adsorption separation has shown a promising future. Herein, a new nanoporous coordination polymer (PCP) adsorbent with fixed and free Cu ions (termed NTU-66-Cu) was prepared through post-synthetic approach via cation exchanging from the pristine NTU-66, an anionic framework with new 3, 4, 6-c topology and two kinds of cages. The NTU-66-Cu shows significantly improved C₂H₂/CO₂ selectivity from 6 to 32 (v/v: 1/1) or 4 to 42 (v/v: 1/4) at low pressure under 298 K, along with enhanced C₂H₂ capacity (from 89.22 to 111.53 cm³·g^-1). More importantly, this observation was further validated by density functional theory (DFT) calculations and breakthrough experiments under continuous and dynamic conditions. Further, the excellent chemical stability enables this adsorbent to achieve recycle C₂H₂/CO₂ separation without loss of C₂H₂ capacity.