Lithium-sulfur (Li-S) batteries have recently emerged as a promising candidate for next-generation energy storage systems. Yet the polysulfide dissolution and shuttle issues cause severe performance degradation, hindering their practical use. Here, we report an in-situ solidification strategy for efficient polysulfide blocking via nucleophilic substitution reactions triggered by 2, 5-dichloro-1, 4-benzoquinone (DCBQ) in the electrolyte. Polysulfides could be covalently fixed by DCBQ in the form of solid organosulfur to enable effective immobilization of polysulfides within the cathode, contributing to high capacity-retention. Moreover, the benzoquinonyl groups of DCBQ were found able to accelerate the lithium-ion transport and promote the sulfur redox reaction kinetics. Consequently, the Li-S cell with DCBQ exhibited good electrochemical performances. This approach demonstrates a novel avenue for polysulfide blocking to boost Li-S battery performance.