The invention relates to an application method of an ionic liquid for removing sulfur from oils. The method comprises the following steps: dissolving chloroalkyl carboxylic acid solid in deionized water and adding pyridine, fully washing with ethyl acetate, carrying out vacuum drying on the synthesized product and then dissolving into the deionized water; slowly dropwise adding concentrated sulfuric acid or concentrated phosphoric acid so as to prepare a pyridine salt ionic liquid for the desulfuration of the oils; adding the ionic liquid and imitated oils containing the sulfur content of 1000ppm, stirring and heating; adding an aqueous hydrogen peroxide solution, cooling to room temperature, and standing for layering, wherein desulfured oils are on the upper layer, carrying out rotary evaporation and reextraction on the ionic liquid on the lower layer so as to respectively achieve dehydration and separation of sulfone compounds, and carrying out vacuum drying so that the ionic liquid can be recycled. By using the method, the defects that the ionic liquid is large in dosage, high in cost and is difficult to meet deep desulfuration are overcome. The method can be used for synthesizing functionalized pyridine salt ionic liquids and used for oil oxidation/extraction deep desulfuration, the dosage of an oxidant is less, desulfuration efficiency is high, the ionic liquid can be recycled, the yield of the oils is high, cost is low, and environment is not polluted.