The practical application of lithium−sulfur (Li–S) batteries has been hindered by the shuttle effect of lithium polysulfides (LiPSs), owing to the high solubility of LiPSs in ether-based electrolyte. Herein, a kind of composite cathode (CC3@S) based on porous organic cages (CC3) through grinding-mechanochemistry and dissolution-precipitation is developed. CC3 possesses the merits of non-carbon element framework and intrinsic inner cavity with open window. These features enable CC3 to achieve a uniform distribution of S based on the host-guest encapsulation process and to offer a favorable dual-function catalytic effect during the redox reaction processes, which accelerates the conversion kinetics of LiPSs. Then, both theoretical and experimental simulation results confirm that CC3 can simultaneously confine LiPSs and suppress their diffusion. Finally, the as-resulted Li–S cell, coupling with CC3@S electrode, displays a high capacity of 523 mAh/g with a CE of 96.2% after 1000th cycle at 1 C. This work proves that the molecular crystal material can be seen as the promising model to reveal the confinement and diffusion of LiPSs for Li–S batteries.