The invention discloses uses of an ionic liquid as a catalyst in preparation of liquid crystal polyesters, particularly performing of a polymerization monomer acylation reaction step and/or a meltingcondensation polymerization reaction step after acylation in liquid crystal polyester preparation reaction steps under the catalysis of an ionic liquid, wherein the ionic liquid is obtained by carrying out a reaction on a heterocyclic organic alkali compound containing two or more nitrogen atoms and an anionic functional compound, and the adding amount of the ionic liquid is 5-2000 ppm based on the total amount of all the added polymerization monomer. According to the present invention, the ionic liquid catalyst has advantages of efficient directional catalytic property, obvious catalytic effect and reduced side reaction of polymerization; the ionic liquid has advantages of excellent stability and long-lasting catalytic effect; the prepared ionic liquid can be directly added to the acylation and transesterification reaction system without purification, such that the operation is simple; and the liquid crystal polyester resin prepared under the catalysis of the ionic liquid catalyst hasexcellent tensile strength and excellent notched impact strength.