The invention relates to a preparation method of a supported ionic liquid catalyst capable of being applied in transesterification of glycerinum and dimethyl carbonate. The catalyst adopts Fe3O4/SiO2 magnetic silica gel as a carrier, after silanization treatment is carried out on the carrier, organic base is loaded on the carrier, and the carrier is reacted with potassium hydroxide to obtain the Fe3O4/SiO2 magnetic silica gel supported basic ionic liquid catalyst. The catalyst prevents the problem that the organic base catalyst is hard to separate in reaction for catalysiscatalized preparation of glycerol carbonate, keeps the characteristics of high activity and high selectivity of the organic base catalyst, is not remarkably inactivated after being recycle for 6 times, and shows the advantages of high activity, easiness in separation, and high stability of the Fe3O4/SiO2 magnetic silica gel supported basic ionic liquid catalyst.