Direct structural information of confined CO in a micropore is important for elucidating its specific binding or activation mechanism. However, weak gas-binding ability and/or poor sample crystallinity after guest exchange hindered the development of efficient materials for CO incorporation, activation and conversion. Here, we present a dynamic porous coordination polymer (PCP) material with local flexibility, in which the propeller-like ligands rotate to permit CO trapping. This process can be characterized by X-ray structural analysis. Owing to its high affinity towards CO and the confinement effect, the PCP exhibits high catalytic activity, rapid transformation dynamics, even high size selectivity to different substrates. Together with an excellent stability with turnover numbers (TON) of up to 39,000 per Zn cluster of catalyst after 10 cycles for CO cycloaddition to form value-added cyclic carbonates, these results demonstrate that such distinctive structure is responsible for visual CO capture and size-selective conversion.