Abstract: A side chain with sulfonate group as end group was bonded on the backbone of polysulfone (PSF) by two steps-"one pot" method. The sulfonation-modified PSF with a micro-phase separation structure was prepared, in which the hydrophobic main-chain and hydrohilic sulfonate groups were in a separate state by locating the sulfonate groups away from the polymer main chains. The Friedel-Cratfs alkylation reaction on benzene ring of PSF backbone was allowed to be carried out with 2-chloroethylisocyanate (CEIC) as electrophilic reagent, and the intermediate polymer PSF-eic, in whose chain the active group —NCO was as electrophilic reagent, and the intermediate polymer PSF-eic, in whose chain the active group —NCO was contained, was obtained. And then a sulfonation-modified polysulfone PSF-sas, in whose side chain sulfonate group was the end group, was prepared through the fast reaction between the active group —NCO and p-hydroxybenzenesulfonic acid sodium (HBSAS). The chemical structure of the target polymer PSF-sas was fully characterized by FT-IR、 1H-NMR and ultraviolet spectrophotometry. PSF cation-exchange membrane was prepared by solution casting method with PSF-sas as membrane material, and the basic properties of the cation-exchange membrane including ion exchange capacity, water uptake and proton conductivity were determined. The experiment results showed that with the action of Lewis acid catalyst, the Friedel-Cratfs alkylation reaction between the benzene ring on the main-chain of PSF and CEIC could be carried smoothly, and the intermediate polymer PSF-eic was formed. The content of ethylisocyanate (eic) group in PSF-eic macromolecular chain could get up to 2.43 mmol/g with dimethylacetamide (DMAC) having strong polarity as solvent and in a reaction period of 24 h. On this basis, through the second step reaction, the target product PSF-sas with a content of sulfonate of 2.23 mmol/g could be obtained. The prepared cation-exchange membrane had higher ion exchange capacity, water uptake with a certain value and higher proton conductivity.