A reaction system and method for producing polyoxymethylene dialkyl ethers (RO(CH₂O)_nR, n=1-8) by continuous acetalation of formaldehyde and aliphatic alcohol in the presence of an acid ionic liquid catalyst. The reaction system includes an acetalation reaction unit, a product separation unit, and a catalyst regeneration unit. The recyclable material and catalyst are separated by combining extraction and rectification, and a recovery rate of more than 99% for the catalyst is achieved. Water, as the byproduct, is separated from the reaction system by destroying the azeotrope of water, alcohol, aldehyde, and RO(CH₂O)_nR, so that the product separation and catalyst regeneration are facilitated and the catalytic cycle is achieved.