Abstract: N-(3-Sulfopropyl) pyridinium methanesulfonate ionic liquid was immobilized on HZSM-5 molecular sieves by chemical method and used as the catalyst in the synthesis of polyoxymethylene dimethyl ethers (PODE_n). X-ray diffraction, infrared spectroscopy and N₂ sorption results showed that the ionic liquid is well immobilized on the molecular sieves. The optimized reaction conditions for the synthesis of PODE_n distributions are obtained, i.e. m(ionic liquid)/m(HZSM-5) = 0.25, n(CH₃OH)/n((CH₂O)₃) = 1.5, 2.2% catalyst, 110 ℃ and 3 h. Under these conditions, the yield of PODE_3~8, as the ideal additives for diesel fuel, reaches 67.35%, which is much higher than those with single ionic liquid or molecular sieve as the catalyst. The immobilized ionic liquid can be easily recycled and reused; the yield of PODE_3~8 remains up to 45.62% after reused for three times.