The shuttling of soluble polysulfides between electrodes is the main factor leading to the rapid capacity fading of Li-S batteries. A functional rich amine porous organic polymer/acetylene black-polypropylene (RAPOP/AB-PP) separator was prepared using a straightforward coating modification of the commercial PP separator to improve the electrochemical performance of Li–S batteries. Electrochemical impedance spectroscopy and discharge/charge tests using S electrodes as research electrodes determined that the abundant amount of imine groups of RAPOPs exhibited strong anchoring properties toward Li polysulfides. The tests also confirmed that the RAPOP/AB-PP separator could effectively inhibit the shuttling of polysulfides. During discharge, the modified separator adsorbed the polysulfides from the electrolyte on the surface of the S electrode and formed a thin layer of Li polysulfide. In addition, this accumulation layer inhibited the diffusion of Li polysulfide through the separator toward the Li electrode. The initial and 800 cycle discharge capacity densities of the RAPOP/AB-PP-1.7 membrane were 1322 and 897 mAh g−1 (at the current density of 0.2 mA cm−2), respectively which were much higher than the 1121 and 481 mAh g−1 corresponding values for the polypropylene separator. In addition, the RAPOP/AB-PP separator possessed a higher electrolyte uptake capacity (114%) than the PP separator (88%). Outstanding electrolyte wettability caused the ion conductivity (1.08 × 10−1 mS cm−1) of the RAPOP/AB-PP membrane to be much higher than that of the PP separator (1.19 × 10−2 mS cm−1). Therefore, the excellent electrochemical performance of the RAPOP/AB-PP separator could be ascribed to the polar RAPOP/AB coating not only alleviating the shuttle effect but also facilitating Li+ ions migration.