Abstract: A sulfonic polymer-based catalyst (PDS-1.0) was synthesized by the hydrothermal and in situ sulfonation method, which is further modified by grafting with CF₃SO₃H, to get the PDS-1.0-F catalyst. The physical and chemical properties of the PDS-1.0 and PDS-1.0-F catalysts were characterized by N₂ sorption, TG, FT-IR, ³¹P MAS NMR and XPS; the effect of CF₃SO₃H modification on the catalytic performance of PDS-1.0-F in the carbonylation of formaldehyde to glycolic acid was then investigated. The results show that after the CF₃SO₃H modification, the framework of PDS-1.0-F catalyst was grafted with strong electron withdrawing groups. In comparison with PDS-1.0, the CF₃SO₃H-modified PDS-1.0-F catalyst has a lower surface area, pore volume and concentration of acid sites, but much stronger acidity and higher thermal stability. As a result, the PDS-1.0-F catalyst exhibits excellent performance in the carbonylation of formaldehyde and over it the yield of glycolic acid reaches 91.2%.