Separation of hydrogen from carbon dioxide for sustainable H₂ production and CO₂ capture still faces great challenges due to the smaller size of H₂ and higher condensability of CO₂. Herein, a high-performance benzimidazole-linked polymer (BILP) membrane for hydrogen separation was directly prepared on α-Al₂O₃ substrate through a facile interfacial polymerization approach at room temperature. The separation performance of the BILP membrane were regulated by controlling the reaction time and the microstructure was systematically characterized. Molecular simulations were performed to deep understand the separation mechanism in the BILP membrane. The best performance membrane displays an extraordinary mixed gas selectivity of 40 for H₂/CO₂ together with outstanding H₂ permeance of 250 gas permeation units (GPU) at 473 K, far exceeding the Robeson's upper bound. Besides, the membrane can withstand high temperature and pressure, and also shows good H₂/N₂ and H₂/CH₄ selectivity. The excellent separation performance, coupled with high temperature and pressure resistance and easy preparation, render BILP membranes great potential for economic H₂ purification, H₂ recovery, and natural gas treatment.