The impediments to the safety and cyclic performance of lithium-sulfur (Li-S) batteries arise from the lithium dendrite growth and “shuttle effect” of polysulfides. Herein, an interfacial engineering was proposed by pre-irradiation grafting acrylic acid (AA) into polypropylene (PP) separator to achieve a dendrite-inhibiting and high stability functional separators. The abundant –COOH groups, introduced to the surface of PP along with AA, effectively modulate lithium dendrite growth by eliminating the local aggregation of Li+ on the surface of the anode and restrain the “shuttle effect” of polysulfides by the physical confinement and electrostatic interaction. Lithium-sulfur batteries with the grafted separator achieved a high initial capacity of 1108.7 mAh g−1 with an ultralow attenuation rate of 0.012 % per cycle at 1C, outperforming the traditional commercial PP separator. Additionally, the grafted separator also appeared a remarkable flexibility owing to the chemical bond between AA and PP-chain. Notably, the pre-irradiation grafting process, characterized by a mild reaction condition and high economic benefit, endowed the grafted separator with outstanding potential for industrialization. Those results showed the practical prospects of the grafted separator, offering a promising new option for high-safety Li-S batteries.